Patent Publication Number: US-9886939-B2

Title: Systems and methods for enhancing a signal-to-noise ratio

Description:
FIELD OF DISCLOSURE 
     This disclosure relates generally to the technical field of electronics, and more specifically, but not exclusively, to methods and apparatus which enhance a signal-to-noise ratio. 
     BACKGROUND 
     Audio in an electronic form can include noise. To a human listener, noise in audio can sound like “hissing,” “wooshing,” or unintelligible crowd noise. Many different mechanisms cause noise in audio, including random Gaussian noise generated by electrical components processing audio, air blowing on a microphone, a microphone or hydrophone detecting movement of fluids such as rain or waves, cosmic background radiation affecting electrical components processing audio, solar radiation affecting electrical components processing audio, electrical storms affecting electrical components processing audio, a vibrating machine (e.g., a fan) near a microphone, and crowds of people talking near a microphone (such as in a restaurant, club, conference hall, concert hall, etc.). Noise is a problem because it interferes with listening to meaningful information in audio. Meaningful information in audio includes speech, music, and other informative sounds. Noise is distracting and can induce a human listener to lose focus on listening to meaningful information in audio. 
     Conventional methods and apparatus, such as audio recording devices, audio processing devices, audio transmission devices, audio amplifying devices, and audio reproduction devices are not sufficiently equipped to mitigate effects of noise. Accordingly, there are previously unaddressed and long-felt industry needs for methods and apparatus which improve upon conventional methods and apparatus. 
     SUMMARY 
     This summary provides a basic understanding of some aspects of the present teachings. This summary is not exhaustive in detail, and is neither intended to identify all critical features, nor intended to limit the scope of the claims. 
     Example methods and apparatus for enhancing a signal-to-noise ratio are provided. In an example, provided is a first apparatus configured to enhance a signal-to-noise ratio. The first apparatus includes a physical processor and a memory communicably coupled to the physical processor. The memory stores instructions configured to cause the physical processor to initiate generating a noise-cancelled digital audio stream from an input digital audio stream. The generating the noise-cancelled digital audio stream includes identifying a noise portion of the input digital audio stream, inverting the identified noise portion, and adding the inverted identified noise portion to the input digital audio stream. The memory also stores instructions configured to cause the physical processor to initiate generating, using at least one intermediate delay reverberator, at least one respective intermediate delay reverberator output from the input digital audio stream. The memory also stores instructions configured to cause the physical processor to initiate generating, using at least one maximum delay reverberator, at least one respective maximum delay reverberator output from the input digital audio stream. Further, the memory stores instructions configured to cause the physical processor to initiate combining the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, and the at least one respective maximum delay reverberator output to form an output digital audio stream having the enhanced signal-to-noise ratio. In an example, the memory further stores instructions configured to cause the processor to initiate normalizing an intensity of the output digital audio stream to substantially an intensity of the input digital audio stream by weighting at least one of the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, or the at least one respective maximum delay reverberator output. In another example, the generating at least one respective intermediate delay reverberator output includes weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one intermediate delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective intermediate delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. A ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In a further example, the generating at least one respective maximum delay reverberator output includes weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one maximum delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective maximum delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. In this further example, a ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In another example, the generating at least one respective maximum delay reverberator output includes delaying the input digital audio stream by a maximum delay in an inclusive range between one sample cycle to thirty sample cycles of the input digital audio stream. In an example, the memory further stores instructions configured to cause the processor to at least one of: initiate attenuating, prior to initiating the combining, the at least one respective intermediate delay reverberator output; or initiate attenuating, prior to initiating the combining, the at least one respective maximum delay reverberator output. In an example, the physical processor is at least one of a microprocessor, a microcontroller, a digital signal processor, a field programmable gate array, a programmable logic device, an application-specific integrated circuit, a controller, a non-generic special-purpose processor, a state machine, a gated logic device, a discrete hardware component, or a dedicated hardware finite state machine, or a combination thereof. In an example, the first apparatus can be a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft. In an example, one or more parts of the first apparatus can be communicatively coupled to a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft. In an example, one or more portions of the first apparatus can be integrated in a semiconductor device, with the semiconductor device optionally being integrated in a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft. 
     In another example, a method for enhancing a signal-to-noise ratio is provided. The method includes generating a noise-cancelled digital audio stream from an input digital audio stream by identifying a noise portion of the input digital audio stream, inverting the identified noise portion, and adding the inverted identified noise portion to the input digital audio stream. The method also includes generating, using at least one intermediate delay reverberator, at least one respective intermediate delay reverberator output from the input digital audio stream. The method further includes generating, using at least one maximum delay reverberator, at least one respective maximum delay reverberator output from the input digital audio stream. The method also includes combining the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, and the at least one respective maximum delay reverberator output to form an output digital audio stream having the enhanced signal-to-noise ratio. In an example, the method includes normalizing an intensity of the output digital audio stream to substantially an intensity of the input digital audio stream by weighting at least one of the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, or the at least one respective maximum delay reverberator output. In an example, the generating at least one respective intermediate delay reverberator output includes weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one intermediate delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective intermediate delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. In this example, a ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In a further example, the generating at least one respective maximum delay reverberator output includes weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one maximum delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective maximum delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. In this further example, a ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In another example, the generating at least one respective maximum delay reverberator output includes delaying the input digital audio stream by a maximum delay in an inclusive range between one sample cycle to thirty sample cycles of the input digital audio stream. In an example, the method further includes at least one of: attenuating, prior to the combining, the at least one respective intermediate delay reverberator output; or attenuating, prior to the combining, the at least one respective maximum delay reverberator output. 
     In another example, provided is a non-transitory computer-readable medium, comprising processor-executable instructions stored thereon. The processor-executable instructions are configured to cause a processor to initiate generating a noise-cancelled digital audio stream from an input digital audio stream. The generating the noise-cancelled digital audio stream includes identifying a noise portion of the input digital audio stream, inverting the identified noise portion, and adding the inverted identified noise portion to the input digital audio stream. The processor-executable instructions are also configured to cause the processor to initiate generating, using at least one intermediate delay reverberator, at least one respective intermediate delay reverberator output from the input digital audio stream. The processor-executable instructions are also configured to cause the processor to initiate generating, using at least one maximum delay reverberator, at least one respective maximum delay reverberator output from the input digital audio stream. Further, the processor-executable instructions are also configured to cause the processor to initiate combining the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, and the at least one respective maximum delay reverberator output to form an output digital audio stream having the enhanced signal-to-noise ratio. In an example, the processor-executable instructions further include instructions configured to cause the processor to initiate normalizing an intensity of the output digital audio stream to substantially an intensity of the input digital audio stream by weighting at least one of the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, or the at least one respective maximum delay reverberator output. In another example, the generating at least one respective intermediate delay reverberator output includes weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one intermediate delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective intermediate delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. A ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In a further example, the generating at least one respective maximum delay reverberator output includes weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one maximum delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective maximum delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. In this further example, a ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In another example, the generating at least one respective maximum delay reverberator output includes delaying the input digital audio stream by a maximum delay in an inclusive range between one sample cycle to thirty sample cycles of the input digital audio stream. In another example, the processor-executable instructions further include instructions configured to cause the processor to at least one of: initiate attenuating, prior to the combining, the at least one respective intermediate delay reverberator output; or initiate attenuating, prior to the combining, the at least one respective maximum delay reverberator output. The non-transitory computer-readable medium, the processor, or both can be integrated with a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft. 
     In another example, provided is a second apparatus configured to enhance a signal-to-noise ratio. The second apparatus includes means for generating a noise-cancelled digital audio stream from an input digital audio stream. The means for generating the noise-cancelled digital audio stream includes means for identifying a noise portion of the input digital audio stream, means for inverting the identified noise portion, and means for adding the inverted identified noise portion to the input digital audio stream. The second apparatus also includes means for generating at least one respective intermediate delay output from the input digital audio stream. The second apparatus also includes means for generating at least one respective maximum delay output from the input digital audio stream. The second apparatus also includes means for combining the noise-cancelled digital audio stream, the at least one respective intermediate delay output, and the at least one respective maximum delay output to form an output digital audio stream having the enhanced signal-to-noise ratio. In an example, the second apparatus includes means for normalizing an intensity of the output digital audio stream to substantially an intensity of the input digital audio stream by weighting at least one of the noise-cancelled digital audio stream, the at least one respective intermediate delay output, or the at least one respective maximum delay output. In an example, the means for generating at least one respective intermediate delay output include means for weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, means for delaying the respective wet-weighted digital audio stream to create at least one respective intervening output, means for weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and means for producing the at least one respective intermediate delay output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. A ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In a further example, the means for generating at least one respective maximum delay output include means for weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, means for delaying the respective wet-weighted digital audio stream to create at least one respective intervening output, means for weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and means for producing the at least one respective maximum delay output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. In this further example, a ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. In another example, the means for generating at least one respective maximum delay output includes means for delaying the input digital audio stream by a maximum delay in an inclusive range between one sample cycle to thirty sample cycles of the input digital audio stream. In an example, the second apparatus includes at least one of: means for attenuating, prior to the combining, the at least one respective intermediate delay output; or means for attenuating, prior to the combining, the at least one respective maximum delay output. The second apparatus can include a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft, of which the means for generating at least one respective intermediate delay output is a constituent part. In an example, one or more parts of the second apparatus can be integrated with a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft. In an example, one or more parts of the second apparatus can be integrated in a semiconductor device, with the semiconductor device optionally being integrated in a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, or a drone aircraft. 
     The foregoing broadly outlines some of the features and technical advantages of the present teachings so the detailed description and drawings can be better understood. Additional features and advantages are also described in the detailed description. The conception and disclosed examples can be used as a basis for modifying or designing other devices for carrying out the same purposes of the present teachings. Such equivalent constructions do not depart from the technology of the teachings as set forth in the claims. The inventive features characteristic of the teachings, together with further objects and advantages, are better understood from the detailed description and the accompanying drawings. Each of the drawings is provided for the purpose of illustration and description only, and does not limit the present teachings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are presented to describe examples of the present teachings, and are not limiting. 
         FIGS. 1A-1B  depicts an example audio processing apparatus configured to enhance a signal-to-noise ratio. 
         FIG. 2  depicts an example method for enhancing a signal-to-noise ratio. 
         FIG. 3  depicts an example device suitable for implementing examples of the disclosed subject matter. 
         FIG. 4  depicts an example impulse response of an example audio processing apparatus. 
         FIG. 5A  depicts an example spectrum of example input audio. 
         FIG. 5B  depicts an example spectrum of example output audio including overtone frequencies. 
         FIG. 6A  depicts example measurements of example input audio. 
         FIG. 6B  depicts example measurements of example output audio having an improved signal-to-noise ratio. 
     
    
    
     In accordance with common practice, the features depicted by the drawings may not be drawn to scale. Accordingly, the dimensions of the depicted features may be arbitrarily expanded or reduced for clarity. In accordance with common practice, some of the drawings are simplified for clarity. Thus, the drawings may not depict all components of a particular apparatus or method. Further, like reference numerals denote like features throughout the specification and figures. 
     DETAILED DESCRIPTION 
     Provided are methods and apparatuses which enhance a signal-to-noise ratio. In an example, provided is an apparatus configured to modify audio to better match the way the human brain processes the audio by modifying the audio to a form which takes advantage of human echolocation capabilities. In an example, the apparatus adds, to the audio, at least one echo of the audio. 
     As humans evolved, they developed echolocation to detect direction and distance of objects, food, and threats. Even today, humans are born with echolocation abilities. Humans perform echolocation by sensing at least one echo of a sound, such as from the sound being reflected from an object, a wall, the like, or a combination thereof. Thus, when humans listen to audio, they subconsciously listen for an echo and thus subconsciously focus on listening to, and for, meaningful echo information in the audio. This focus causes humans to ignore noise in the audio, which results in enhancing a signal-to-noise ratio. 
     The examples disclosed hereby advantageously address the long-felt industry needs, as well as other previously unidentified needs, and mitigate shortcomings of conventional techniques. Among other advantages, an advantage provided by the examples is an improvement in signal-to-noise ratio over conventional devices. The systems and methods described herein can improve the functioning of devices configured to process audio, improve the performance of devices configured to process audio, or both. Moreover, the systems and methods described herein can improve the functioning of devices configured to reproduce audio, improve the performance of devices configured to reproduce audio, or both. The disclosed systems and methods can also improve the fields of audio processing and audio reproduction by enhancing a signal-to-noise ratio, better matching audio to the way the human brain processes audio, improving a user-machine interface, improving an experience of a human listening to the audio, or a combination thereof. 
     Numerous examples are disclosed in this application&#39;s text and drawings. Alternate examples can be devised without departing from the scope of this disclosure. Additionally, conventional elements of the current teachings may not be described in detail, or may be omitted, to avoid obscuring aspects of the current teachings. 
     The following list of abbreviations, acronyms, and terms is provided to assist in comprehending the current disclosure, and are not provided as limitations. 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                   
                 dB - Decibel 
               
               
                   
                 HPF - High Pass Filter 
               
               
                   
                 Hz - Hertz 
               
               
                   
                 LPF - Low Pass Filter 
               
               
                   
               
            
           
         
       
     
     This description provides, with reference to  FIGS. 1A, 1B, and 3 , detailed descriptions of example apparatus for enhancing a signal-to-noise ratio. Detailed descriptions of an example method are provided in connection with  FIG. 2 . 
       FIGS. 1A-1B  depict a block diagram of an example audio processing apparatus  100  configured to enhance a signal-to-noise ratio. The audio processing apparatus  100  can enhance a signal-to-noise ratio by performing at least a portion of the methods, sequences, algorithms, the like, or a combination thereof. The example audio processing apparatus  100  can be implemented at least in part directly in hardware, at least in part by a processor configured to execute stored instructions, or a combination of both. In addition, an electrical circuit of at least a portion of the audio processing apparatus  100  can be implemented as a digital logic circuit configured to perform a described action. 
     Referring to  FIG. 1A , the audio processing apparatus  100  can include elements including an optional first low pass filter  105  (LPF), a splitter  110 , a canceller  115 , a first weighter  120 , optional first meters  125 , a summer  130 , an imager  135 , optional second meters  140 , a second weighter  145 , optional third meters  150 , an optional high pass filter  155  (HPF), and an optional second low pass filter  160 . These elements are described in further detail herein. 
     The optional first low pass filter  105  receives input audio, such as a digital audio stream or an analog audio stream, and filters the input audio. The first low pass filter  105  can be configured to receive a respective user input (e.g., from the user interface  325  depicted in  FIG. 3 ) indicating a respective filter cutoff frequency. In examples, a bandpass filter or a high-pass filter can replace the first low pass filter  105  and filtering the input audio. In an example, the first low pass filter  105  has a cutoff frequency of substantially 18000 Hz. 
     The input audio can have a single channel or multiple channels. In an example, the input audio is two-channel stereo audio. In another example, the input audio is two-channel monaural audio. The two-channel configuration depicted in  FIGS. 1A-1B  is an illustrative example, and is not limiting. 
     The splitter  110  splits the output of the first low pass filter  105  into at least two paths—a first path to the canceller  115  and a second path to the imager  135 . In an example, the audio sent to the canceller  115  and the images  135  is at least essentially identical. In an example, the splitter  110  splits monoaural input audio which is input to the audio processing apparatus  100  into multiple channels (e.g., a left channel and a right channel). 
     The canceller  115  generates noise-cancelled audio. The canceller  115  reduces noise to increase the effectivity of the audio processing apparatus  100 . In an example, the canceller  115  identifies a noise portion of the audio input to the canceller  115 , inverts the identified noise portion, and adds the inverted identified noise portion to the audio input to the canceller  115 . 
     In an example, the audio input to the canceller  115  is attenuated (e.g., by −18 dB) to form intermediate audio characterized by reduced intensity (e.g., volume level). This effectively isolates meaningful information having a higher intensity from noise having a lower intensity. The intermediate audio is inverted and combined with the audio input to the canceller  115  to isolate a noise portion. The isolated noise portion is attenuated (e.g., by −18 dB). The isolated noise portion is then inverted and combined with the audio input to the canceller  115  to generate the noise-cancelled audio. 
     The noise-cancelled audio initially presents a sound in the output audio (i.e., “OUT” in  FIG. 1A ), and thus, for a human listener, is a timing reference for comparison of one or more subsequent echoes of the sound. 
     The optional first weighter  120  weights (e.g., adjusts by amplifying or attenuating) the noise-cancelled audio to balance audio intensity of the noise-cancelled audio which is input to the summer  130  with the intensity of audio input to the summer  130  from the second meters  140 . Balancing the audio can prevent peaking and clipping in the output audio. In an example, the first weighter  120  attenuates the noise-cancelled audio by an amount in an inclusive range between substantially +1 dB to substantially −18 dB. In an example, the first weighter  120  attenuates the noise-cancelled audio by −3 dB. In an example, a weight applied by the first weighter  120  can be dynamic, with a change in the applied weight being based on a change in intensity of the input audio (e.g., at the input to the first LPF  105 , the splitter  110 , or the like). In another example, the applied weight can be user-selected and based on received selection information. 
     The optional first meters  125  measure intensity of the noise-cancelled audio and provide intensity information which can be displayed on a display, such as a display  320  depicted in  FIG. 3 . 
     The summer  130  forms output audio having the enhanced signal-to-noise ratio by combining (e.g., by adding) the noise-cancelled audio with at least one respective intermediate delay reverberator output, and at least one respective maximum delay reverberator output from the imager  135 . 
     The imager  135  generates the at least one respective intermediate delay reverberator output, and the at least one respective maximum delay reverberator output. We now turn to  FIG. 1B . 
       FIG. 1B  illustrates an example block diagram of the imager  135 , including a reverberator element  165  including one or more reverberators, such as reverberators  170 ( 1 )-( 4 ), an expander element  175  including one or more expanders, such as expanders  180 ( 1 )-( 4 ), and a weighter element  185  including one or more weighters, such as weighters  190 ( 1 )-( 4 ). 
     The reverberator element  165  includes at least one reverberator which is configured to delay audio supplied to the summer  130  to produce at least one echo in the output audio. When humans listen to the output audio, they subconsciously listen for the echo and thus subconsciously focus on listening to, and for, meaningful echo information in the output audio. This focus causes humans to ignore noise in the output audio, which results in enhancing a signal-to-noise ratio. In an example, a reverberator can be replaced by a delay line. In another example, each reverberator can create a respective echo to simulate a reflection of the input audio from a simulated wall in a simulated room. In an example, one or more generated echoes includes a frequency within a human hearing range. In an example, the human hearing range can be within an inclusive range between 20 Hz to 24000 Hz. In another example, the human hearing range can be within an inclusive range between substantially 20 Hz to substantially 20000 Hz. 
     In the example in  FIG. 1B , the reverberator element  165  has four reverberators  170 ( 1 )- 170 ( 4 ). The reverberator element  165  has two optional intermediate delay reverberators  170 ( 1 )-( 2 ) and two maximum delay reverberators  170 ( 3 )-( 4 ). 
     In examples, other quantities of reverberators can be implemented. An example can include one or more reverberators per channel, one or more reverberators per one or more respective delay times, or combinations thereof. 
     The intermediate delay reverberators  170 ( 1 )-( 2 ) generate at least one respective intermediate delay reverberator output from the audio received from the splitter  110 . The intermediate delay reverberator output provides audio which is an echo, relative to the noise-cancelled audio supplied to the summer  130 . The intermediate delay reverberator output provides an echo having a shorter delay than an echo provided by the maximum delay reverberator output. 
     In an example, the intermediate delay reverberators  170 ( 1 )-( 2 ) generate the at least one respective intermediate delay reverberator output at least in part by (1) weighting the audio received from the splitter  110  with a respective wet weight to produce respective wet-weighted audio, (2) reverberating the respective wet-weighted audio with the at least one intermediate delay reverberator to create at least one respective intervening output, (3) weighting the audio received from the splitter  110  with a respective dry weight to produce respective dry-weighted audio, and (4) producing the at least one respective intermediate delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted audio. 
     The wet weight is an attenuation applied to audio which is subsequently reverberated. The dry weight is an attenuation applied to audio which is not reverberated, and is subsequently combined with reverberated audio. The wet weight, in cooperation with the dry weight, determines a proportion between a quantity of audio which is reverberated and a quantity of audio which is not reverberated. A ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. 
     The maximum delay reverberators  170 ( 3 )-( 4 ) generate at least one respective maximum delay reverberator output from the audio received from the splitter  110 . The maximum delay reverberator output provides audio which is an echo, relative to the noise-cancelled audio supplied to the summer  130 . The maximum delay reverberator output provides an echo having a longer delay than an echo provided by the intermediate delay reverberator output. 
     In an example, maximum delay reverberators  170 ( 3 )-( 4 ) generate the at least one respective maximum delay reverberator output at least in part by (A) weighting the audio received from the splitter  110  with a respective wet weight to produce a respective wet-weighted audio, (B) reverberating the respective wet-weighted audio with the at least one maximum delay reverberator to create at least one respective intervening output, (C) weighting the audio received from the splitter  110  with a respective dry weight to produce a respective dry-weighted audio stream, and (D) producing the at least one respective maximum delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted audio. A ratio of the respective dry weight to the respective wet weight can be in an inclusive range between one-to-one and twenty-to-one. 
     In an example, generating the at least one respective maximum delay reverberator output includes the maximum delay reverberators  170 ( 3 )-( 4 ) delaying the audio received from the splitter  110  by a maximum delay in an inclusive range between one sample cycle of the audio received from the splitter  110  to thirty sample cycles of the audio received from the splitter  110 . A sample cycle, also known as a sampling interval and a sampling period, is a period of time between taking discrete samples of a continuous waveform to form the input digital audio stream. In an example, if the audio received from the splitter  110  has a sample rate of 44,100 Hz, then the sample cycle has a duration of 1/(44,100 seconds −1 )=0.0000226757 seconds. In examples, the audio received from the splitter  110  has a sample rate other than 44,100 Hz. 
     In an example, the maximum delay of the maximum delay reverberators  170 ( 3 )-( 4 ) is long enough to provide the maximum delay reverberator output at a time to which human echolocation is sensitive. In an example, the maximum delay of the maximum delay reverberators  170 ( 3 )-( 4 ) is short enough to provide the maximum delay reverberator output at a time to which a human does not consciously perceive reverberation of the audio. 
     The optional expander element  175  includes at least two expanders which are configured to attenuate respective left and right channels of the intermediate delay reverberator output and respective left and right channels of the maximum delay reverberator output. Reducing the respective intensities between left and right channels produces moving echoes (i.e., echoes with diminishing intensity). When humans listen to the output audio, they subconsciously focus on listening to the moving echoes, which induces focus on meaningful echo information in the output audio, thus enhancing a signal-to-noise ratio. 
     In the example in  FIG. 1B , the expander element  175  includes four expanders. Expanders  180 ( 1 )- 180 ( 2 ) weight (e.g., attenuate or amplify) respective right and left channels of the intermediate delay reverberator output by different amounts. Expanders  180 ( 3 )- 180 ( 4 ) weight (e.g., attenuate or amplify) respective right and left channels of the maximum delay reverberator output by different amounts. In an example, the expanders  180 ( 1 )- 180 ( 4 ) attenuate by an amount in an inclusive range between 0.1% to 99.9%. 
     In an example, the expanders  180 ( 1 )- 180 ( 2 ) can attenuate the right channel of the intermediate delay reverberator output by 44% and can attenuate the left channel of the intermediate delay reverberator output by 17%. This combination of attenuations of the right channel of the intermediate delay reverberator output and the left channel of the intermediate delay reverberator output simulate an echo from a location in front, and slightly left of center of a listener. The expanders  180 ( 3 )- 180 ( 4 ) can attenuate the right channel of the maximum delay reverberator output by 90% and can attenuate the left channel of the maximum delay reverberator output by 0.5%. This combination of attenuations of the right channel of the intermediate delay reverberator output and the left channel of the intermediate delay reverberator output simulate an echo from a location from the left and slightly to the rear of the listener. These example attenuations are not limiting. In other examples, other attenuations can be implemented. For example, another attenuation can be implemented to simulate a respective echo from another location relative to a listener. 
     The optional weighter element  185  includes at least two weighters which are configured to attenuate (or amplify) the intermediate delay reverberator output and the maximum delay reverberator output. Reducing the respective intensities of the intermediate delay reverberator output and the maximum delay reverberator output, relative to the noise-cancelled audio supplied to the summer  130 , produces fading echoes (i.e., echoes with diminishing intensity). When humans listen to the output audio, they subconsciously focus on listening to the fading echoes, which induces focus on meaningful echo information in the output audio, thus enhancing a signal-to-noise ratio. In an example, a weight applied by a respective weighter in the weighter element  185  can be dynamic, with a change in the applied weight being based on a change in intensity of the input audio. In another example, the applied weight can be user-selected and based on a received user selection of the applied weight. 
     In the example in  FIG. 1B , the weighter element  185  includes four weighters—first and second weighters  190 ( 1 )- 190 ( 2 ) weight the intermediate delay reverberator output and third and fourth weighters  190 ( 3 )- 190 ( 4 ) weight the maximum delay reverberator output. 
     The first and second weighters  190 ( 1 )- 190 ( 2 ) and the third and fourth weighters  190 ( 3 )- 190 ( 4 ) weight (e.g., respectively amplify or respectively attenuate) a respective audio intensity of a respective channel. For example, the first weighter  190 ( 1 ) and the third weighter  190 ( 3 ) weight respective right channels, and the second weighter  190 ( 2 ) and the fourth weighter  190 ( 4 ) weight respective left channels. In a further example, the first weighter  190 ( 1 ) and the third weighter  190 ( 3 ) weight respective left channels, and the second weighter  190 ( 2 ) and the fourth weighter  190 ( 4 ) weight respective right channels. 
     In an example, the first and second weighters  190 ( 1 )- 190 ( 2 ) and the third and fourth weighters  190 ( 3 )- 190 ( 4 ) respectively attenuate by an amount in an inclusive range between substantially +1 dB to substantially −32 dB. In a non-limiting example, the weighters  190 ( 1 )- 190 ( 2 ) attenuate the intermediate delay reverberator output by −6 dB and the weighters  190 ( 3 )- 190 ( 4 ) weight the maximum delay reverberator output by −18 dB. In other examples, other attenuations can be implemented. For example, a user-selected attenuation can be implemented. In examples, the maximum delay reverberator output is attenuated more than the intermediate delay reverberator output to produce a fading series of echoes. 
     In an example, the intensity adjustments provided by the expander element  175  are performed by the weighter block  185 . In another example, the intensity adjustments provided by the weighter block  185  are performed by the expander element  175 . 
     Returning to  FIG. 1A , the optional second meters  140  measure intensity of the at least one respective intermediate delay reverberator output, at least one respective maximum delay reverberator output, or both. The optional second meters  140  provide intensity information which can be displayed on a display, such as the display  320  in  FIG. 3 . 
     Again, the summer  130  forms the output audio having the enhanced signal-to-noise ratio by combining (e.g., by adding) the noise-cancelled audio originating in the canceller  115  with at least one respective intermediate delay reverberator output originating in the imager  135 , and at least one respective maximum delay reverberator output originating in the imager  135 . The combining of the noise-cancelled audio with the at least one respective intermediate delay reverberator output originating in the imager  135 , and the at least one respective maximum delay reverberator output originating in the imager  135  can generate at least one overtone in the output audio. 
     In an example, the overtones are a product of an echo being combined (i.e., mixed) with the noise-cancelled audio. The combination can create the overtones (i.e., a harmonic resonance) due to periodic phase synchronization between respective waveforms of the echo and the noise-cancelled audio. The overtones generated by the audio processing apparatus  100  can include beat frequencies generated by the echo and the noise-cancelled audio beating against each other. The overtones generated by the echo can increase the intensity of meaningful information in the output audio at a time when the echo is present. For example, if the input audio includes meaningful information such as speech having a hard consonant, a hard syllable, etc., the overtones increase an intensity associated with the hard consonant, the hard syllable, etc. Accordingly, the intensity of meaningful information in the output audio increases relative to the intensity of noise in the output audio, which increases the signal-to-noise ratio. An empirical example of an impact of overtones on intensity of meaningful information in output audio is depicted and described herein in reference to  FIGS. 5A-5B . An empirical example of an impact of overtones on signal-to-noise ratio in output audio is depicted and described herein in reference to  FIGS. 6A-6B . 
     The optional second weighter  145  weights (e.g., attenuates or amplifies) an intensity of the audio from the summer  130  to normalize the intensity of the output audio to substantially match an intensity of the input audio. The second weighter  145  can receive an input (not shown, e.g., from the splitter  110 ) indicating the intensity of the input audio to use as a reference when normalizing. In an example, the second weighter  145  attenuates an intensity of the audio from the summer  130  by an amount in a range between substantially +1 dB to substantially −18 dB. In an example, the first weighter  120  attenuates the noise-cancelled audio by −3 dB. In an example, a weight applied by the second weighter  145  can be dynamic, with a change in the applied weight being based on a change in intensity of the input audio. In another example, the applied weight can be user-selected and based on a received user selection. 
     The optional third meters  150  measure a volume level and can provide volume level information which can be displayed on a display, such as the display  320  in  FIG. 3 . 
     The optional high pass filter  155  provides high-pass filtering. The high pass filter  155  can be configured to receive a respective user input (e.g., from the user interface  325  depicted in  FIG. 3 ) indicating a respective filter cutoff frequency. In examples, a bandpass filter or a low-pass filter can replace the high pass filter  155  and filter the output audio. 
     The optional second low pass filter  160  provides low-pass filtering. The second low pass filter  160  can be configured to receive a respective user input (e.g., from the user interface  325  depicted in  FIG. 3 ) indicating a respective filter cutoff frequency. In examples, a bandpass filter or a high-pass filter can replace the second low pass filter  160  and filter the output audio. In an example, the second low pass filter  160  has a cutoff frequency of substantially 18000 Hz. 
     In an example, the output audio from the audio processing apparatus  100  (“OUT” in  FIG. 1A ) (e.g., audio output from the second low pass filter  160 ) has a number of channels equal to the number of channels in the input audio which is input to the audio processing apparatus  100 . In another example, the output audio from the audio processing apparatus  100  is not phase inverted relative to the input audio which is input to the audio processing apparatus  100 . 
     The output audio from the audio processing apparatus  100  can be stored—for example, referring to  FIG. 3 , by memory  315 , fixed storage  330 , removable storage  335 , network device  350 , the like, or a combination thereof. The output audio from the audio processing apparatus  100  can be transmitted—for example, referring to  FIG. 3 , by user interface  325 , network interface  340 , the like, or a combination thereof. The output audio from the second low pass filter  160  can be reproduced—for example, referring to  FIG. 3 , by a speaker, headphones, an audio reproduction device, an audio processing device, the like, or a combination thereof coupled to the user interface  325 , the network interface  340 , the like, or a combination thereof. 
     In an example, one or more parts of the audio processing apparatus  100  can be a part of a system, communicatively coupled to a system, or both, where the system is a device configured to generate audio, convert audio, transmit audio, receive audio, store audio, process audio, reproduce audio, the like, or a combination thereof. In examples, the system can be a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, a drone aircraft, or a practicable combination thereof. 
       FIG. 2  depicts an example method which enhances a signal-to-noise ratio  200 . The method for enhancing a signal-to-noise ratio  200  can be performed by the apparatus described hereby, such as the audio processing apparatus  100  in  FIGS. 1A-1B , the example computing device  300  in  FIG. 3 , or a practicable combination thereof. 
     In block  205 , a noise-cancelled digital audio stream is generated from an input digital audio stream by identifying a noise portion of the input digital audio stream, inverting the identified noise portion, and adding the inverted identified noise portion to the input digital audio stream. 
     The input digital audio stream can have a single channel or multiple channels. In an example, the input digital audio stream is two-channel stereo audio. In another example, the input digital audio stream is two-channel monaural audio. The two-channel configuration depicted in  FIGS. 1A-1B  is an illustrative example, and is not limiting. 
     In block  210 , at least one respective intermediate delay reverberator output is generated from the input digital audio stream. The at least one respective intermediate delay reverberator output can be generated using at least one intermediate delay reverberator. 
     In an example, the at least one respective intermediate delay reverberator output is generated at least in part by weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one intermediate delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective intermediate delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. The wet weight is an attenuation applied to audio which is subsequently reverberated. The dry weight is an attenuation applied to audio which is not reverberated, and is subsequently combined with reverberated audio. The wet weight, in cooperation with the dry weight, determines a proportion between a quantity of audio which is reverberated and a quantity of audio which is not reverberated. A ratio of the respective dry weight to the respective wet weight can be in a range between one-to-one and twenty-to-one. 
     In block  215 , at least one respective maximum delay reverberator output is generated from the input digital audio stream. The at least one respective maximum delay reverberator output can be generated using at least one maximum delay reverberator. 
     In an example, the at least one respective maximum delay reverberator output is generated at least in part by weighting the input digital audio stream with a respective wet weight to produce a respective wet-weighted digital audio stream, reverberating the respective wet-weighted digital audio stream with the at least one maximum delay reverberator to create at least one respective intervening output, weighting the input digital audio stream with a respective dry weight to produce a respective dry-weighted digital audio stream, and producing the at least one respective maximum delay reverberator output by combining the at least one respective intervening output with the respective dry-weighted digital audio stream. A ratio of the respective dry weight to the respective wet weight can be in a range between one-to-one and twenty-to-one. 
     In an example, generating the at least one respective maximum delay reverberator output includes delaying the input digital audio stream by a maximum delay in an inclusive range between one sample cycle of the input digital audio stream to thirty sample cycles of the input digital audio stream. A sample cycle, also known as a sampling interval and a sampling period, is a period of time between taking discrete samples of a continuous waveform to form the input digital audio stream. In an example, if the input digital audio stream has a sample rate of 44,100 Hz, then the sample cycle has a duration of 1/(44,100 seconds −1 )=0.0000226757 seconds. In an example, the maximum delay is long enough to provide the maximum delay reverberator output at a time to which human echolocation is sensitive. In an example, the maximum delay is short enough to provide the maximum delay reverberator output at a time to which a human does not consciously perceive reverberation of the audio. 
     In optional block  220 , the at least one respective intermediate delay reverberator output is attenuated prior to the combining, the at least one respective maximum delay reverberator output is attenuated prior to the combining, or both. 
     In block  225 , the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, and the at least one respective maximum delay reverberator output are combined to form an output digital audio stream having the enhanced signal-to-noise ratio. 
     In optional block  230 , an intensity of the output digital audio stream is normalized to substantially an intensity of the input digital audio stream by weighting at least one of the noise-cancelled digital audio stream, the at least one respective intermediate delay reverberator output, or the at least one respective maximum delay reverberator output. 
     The blocks in  FIG. 2  are not limiting of the examples. The blocks can be combined, the order can be rearranged, or both, as practicable. 
     Examples of the disclosed subject matter can be implemented in, and used with, hardware devices, network architectures, the like, and a combination thereof.  FIG. 3  illustrates the example computing device  300  suitable for implementing examples of the disclosed subject matter. In an example, the computing device  300  can be a desktop computer, a laptop computer, a mobile device, a special-purpose computer, a non-generic computer, an electronic device described hereby (as is practicable), the like, or a combination thereof. In an example, the computing device  300  can be a hearing aid, an x-ray machine, a wireless router, a cell site device, a satellite, a space-based telescope, a missile guidance system, a sonar system, a cellular phone, a personal computer, a mixing board, a sound system, an amplifier, a car, a home appliance, a night-vision goggle, an augmented reality device, a virtual reality device, a laser-based eye surgery device, a radio device, a quantum computing device, a camera, a television, a radar device, a drone aircraft, the like, or a practicable combination thereof. 
     The computing device  300  can include a processor  305 , a bus  310 , the memory  315 , the display  320 , the user interface  325 , the fixed storage device  330 , the removable storage device  335 , the network interface  340 , the like, or a combination thereof. 
     The processor  305  is a hardware-implemented processing unit configured to control at least a portion of operation of the computing device  300 . The processor  305  can perform logical and arithmetic operations based on processor-executable instructions stored within the memory  315 . The processor  305  can be configured to execute instructions which cause the processor  305  to initiate at least a part of a method described hereby. In an example, the processor  305  can interpret instructions stored in the memory  315  to initiate at least a part of a method described hereby. In an example, the processor  305  can execute instructions stored in the memory  315  to initiate at least a part of a method described hereby. The instructions, when executed by the processor  305 , can transform the processor  305  into a special-purpose processor that causes the processor to perform at least a part of a function described hereby. The processor  305  may also be referred to as a central processing unit (CPU), a special-purpose processor (e.g., a non-generic processor), or both. 
     The processor  305  can comprise or be a component of a physical processing system implemented with one or more processors. The processor  305  can be implemented with at least a portion of: a microprocessor, a microcontroller, a digital signal processor (DSP) integrated circuit, a field programmable gate array (FPGA), a programmable logic device (PLD), an application-specific integrated circuit (ASIC), a controller, a state machine, a gated logic circuit, a discrete hardware component, a dedicated hardware finite state machine, a suitable physical device configured to manipulate information (e.g., calculating, logical operations, the like, or a combination thereof), the like, or a combination thereof. 
     The bus  310  couples components of the computing device  300 . The bus  310  can enable information communication between the processor  305  and one or more components coupled to the processor  305 . The bus  310  can include a data bus, a power bus, a control signal bus, a status signal bus, the like, or a combination thereof. In an example, the components of the computing device  300  can be coupled together to communicate with each other using a different suitable mechanism. 
     The memory  315  generally represents any type or form of volatile storage device, non-volatile storage device, medium, the like, or a combination thereof. The memory  315  is capable of storing data, processor-readable instructions, the like, or a combination thereof. In an example, the memory  315  can store data, load data, maintain data, or a combination thereof. In an example, the memory  315  can store processor-readable instructions, load processor-readable instructions, maintain processor-readable instructions, or a combination thereof. The memory  315  can be a main memory configured to store an operating system, an application program, the like, or a combination thereof. The memory  315  can be configured to store a basic input-output system (BIOS) which can control basic hardware operation such as interaction of the processor  305  with peripheral components. The memory  310  can also include a non-transitory machine-readable medium configured to store software. Software can mean any type of instructions, whether referred to as at least one of software, firmware, middleware, microcode, hardware description language, the like, or a combination thereof. Processor-readable instructions can include code (e.g., in source code format, in binary code format, executable code format, or in any other suitable code format). 
     The memory  315  can include at least one of read-only memory (ROM), random access memory (RAM), a flash memory, a cache memory, an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a register, a hard disk drive (HDD), a solid-state drive (SSD), an optical disk drive, other memory, the like, or a combination thereof which is configured to store information (e.g., data, processor-readable instructions, software, the like, or a combination thereof) and is configured to provide the information to the processor  305 . 
     The video display  320  can include a component configured to visually convey information to a user of the computing device  300 . In examples, the video display  320  is a display screen, such as a light-emitting diode (LED) screen. 
     The user interface  325  can include user devices such as a switch, a keypad, a touch screen, a microphone, a speaker, an audio reproduction device, a jack for coupling the computing device to an audio reproduction device, the like, or a combination thereof. The user interface  325  can optionally include a user interface controller. The user interface  325  can include a component configured to convey information to a user of the computing device  300 , a component configured to receive information from the user of the computing device  300 , or both. 
     The fixed storage device  330  can include one or more hard drive, flash storage device, the like, or a combination thereof. The fixed storage device  330  can be an information storage device which is not configured to be removed during use. The fixed storage device  330  can optionally include a fixed storage device controller. The fixed storage device  330  can be integral with the computing device  300  or can be separate and accessed through an interface. 
     The removable storage device  335  can be integral with the computing device  300  or can be separate and accessed through other interfaces. The removable storage device  335  can be an information storage device which is configured to be removed during use, such as a memory card, a jump drive, a flash storage device, an optical disk, the like, or a combination thereof. The removable storage device  335  can optionally include a removable storage device controller. The removable storage device  335  can be integral with the computing device  300  or can be separate and accessed through an interface. 
     Non-transient computer-executable instructions configured to cause a processor to implement at least an aspect of the present disclosure can be stored on a computer-readable storage medium such as one or more of the memory  315 , the fixed storage device  330 , the removable storage device  335 , a remote storage location, the like, or a combination thereof. 
     The network interface  340  can couple the computing device  300  to a network  345  and enable exchanging information between the computing device  300  and the network  345 . For example, the network interface  340  can enable the computing device  300  to communicate with one or more other network devices  350 . The network interface  340  can couple to the network  345  using any suitable technique and any suitable protocol. Example techniques and protocols the network interface  340  can be configured to implement include digital cellular telephone, WiFi™, Bluetooth®, near-field communications (NFC), the like, or a combination thereof. 
     The network  345  can couple the computing device  300  to one or more other network devices. The network  345  can enable exchange of information between the computing device  300  and the one or more other network devices  350 . The network  345  can include one or more private networks, local networks, wide-area networks, the Internet, other communication networks, the like, or a combination thereof. In an example, the network  345  is a wired network, a wireless network, an optical network, the like, or a combination thereof. 
     The one or more other network devices  350  can store computer-readable instructions configured to cause a processor (e.g., the processor  305 ) to initiate performing at least a portion of a method described hereby. In an example, the one or more other network devices  350  can store a first digital audio file. The first digital audio file can be received by the processor  305  and processed using at least a portion of techniques described hereby. In another example, a second digital audio file can be created by the processor  305  using techniques described hereby and stored in the fixed storage device  330 , the removable storage device  335 , the one or more other network devices  350 , the like, or a combination thereof. 
     The one or more other network devices  350  can include a server, a storage medium, the like, or a combination thereof. When the one or more other network devices  350  is a server, the first digital audio file can be received by the server and processed using at least a portion of techniques described hereby. In another example, a second digital audio file can be created by the server using techniques described hereby and stored in the fixed storage device  330 , the removable storage device  335 , the one or more other network devices  350 , the like, or a combination thereof. 
     In examples, the one or more other network devices  350  include a speaker, headphones, an audio reproduction device, an audio processing device, the like, or a combination thereof. Thus, audio processed using the techniques described hereby can be reproduced via the speaker, the headphones, the audio reproduction device, or a combination thereof. In an example, the reproducing can be performed for a human. 
     All of the components illustrated in  FIG. 3  need not be present to practice the present disclosure. Further, the components can be coupled in different ways from those illustrated. 
       FIGS. 4, 5A-5B, and 6A-6B  depict non-limiting empirical examples relating to implementing an embodiment of the audio processing apparatus  100 . 
       FIG. 4  depicts a non-limiting example impulse response  400  of the embodiment of the audio processing apparatus  100 . Further,  FIG. 4  depicts that the example impulse response  400  of the embodiment of the audio processing apparatus  100  is linear. At substantially time zero, the embodiment of the audio processing apparatus  100  receives input audio having an input impulse  405 . The input impulse  405  triggers the embodiment of the audio processing apparatus  100  to generate, at substantially time one, a response  410  in the output audio that includes noise-cancelled audio. The input impulse  405  also triggers the embodiment of the audio processing apparatus  100  to generate an echo  415  of the input impulse  405 . In response, the embodiment of the audio processing apparatus  100  generates the echo  415  at substantially time four. In the example of  FIG. 4 , time is measured in sample cycles. Thus, noise-cancelled audio is output substantially one sample cycle after the embodiment of the audio processing apparatus  100  receives the input impulse  405 . The echo  415  is output substantially three sample cycles after the embodiment of the audio processing apparatus  100  receives the input impulse  405 . 
       FIGS. 5A-5B  depict empirical examples showing the example embodiment of the audio processing apparatus  100  can increase a signal-to-noise ratio. The signal-to-noise ratio increases because the example embodiment of the audio processing apparatus  100  increases intensity of meaningful information in the output signal by generating overtones from echoes.  FIG. 5A  depicts a spectrum of example input audio  500  which is input to the embodiment of the audio processing apparatus  100 . The spectrum of example input audio  500  depicts input audio lacking intensity from approximately 10500 Hz to approximately 11500 Hz. The example embodiment of the audio processing apparatus  100  generates echoes and respective overtones from the input audio. We now turn to  FIG. 5B , which depicts a spectrum of example output audio  505  including overtones created by the audio processing apparatus  100 . As can be seen in  FIG. 5B , the overtones increase an intensity of meaningful information at frequencies including the range from approximately 10500 Hz to approximately 11500 Hz, thus increasing the signal-to-noise ratio of the example output audio. 
       FIGS. 6A-6B  depict empirical examples showing the example embodiment of the audio processing apparatus  100  can increase the signal-to-noise ratio in output audio.  FIGS. 6A-6B  also depict an empirical example of an impact of overtones on signal-to-noise ratio in the output audio. The examples in  FIGS. 6A-6B  are not limiting. 
       FIG. 6A  depicts input measurements  600  of example empirical input audio which can be input to the embodiment of the audio processing apparatus  100 . The input measurements  600  include an input heatmap  605  indicating intensity of the input audio at different times and frequencies. The horizontal axis of the input heatmap  605  indicates time, while the vertical axis of the input heatmap  605  indicates frequency. The selection box  610  indicates a selected portion of the input audio whose characteristics are displayed by the input heatmap  605 . 
     The input heatmap  605  depicts that the input audio includes meaningful information  615  during a portion of time. The input heatmap  605  also depicts the meaningful information  615  has low intensities in the frequencies between approximately 9646 Hz to approximately 12575 Hz, relative to respective intensities occurring at other frequencies outside this range during the portion of time. 
       FIG. 6A  also depicts the signal-to-noise ratio of the input audio, at a time indicated by a cursor  620 , as having a signal portion of −67 dB and a noise portion of −70 dB. 
       FIG. 6B  depicts output measurements  625  of example empirical output audio from the embodiment of the audio processing apparatus  100  resulting from the example empirical input audio from  FIG. 6A  being input to the example embodiment of the audio processing apparatus  100 . The output measurements  625  include an output heatmap  630  indicating intensity of the output audio at different times and frequencies. The horizontal axis of the output heatmap  630  indicates time, while the vertical axis of the output heatmap  630  indicates frequency. The selection box  610  indicates that the selected portion of the input audio whose characteristics are displayed by the output heatmap  630  is substantially the same as the selected portion of the input audio whose characteristics are displayed by the input heatmap  605 . 
     The output heatmap  630  depicts that the output audio includes meaningful information  635  during the portion of time. The output heatmap  630  also depicts the meaningful information  635  has a higher intensity in the frequencies between approximately 9646 Hz to approximately 12575 Hz, relative to the respective lower intensities depicted in  FIG. 6A . The meaningful information  635  has a higher intensity in the frequencies between approximately 9646 Hz to approximately 12575 Hz due to overtones, generated by the example embodiment of the audio processing apparatus  100 , at the frequencies between approximately 9646 Hz to approximately 12575 Hz. 
     Thus, because the intensity of the meaningful information  635  increases at the frequencies between approximately 9646 Hz to approximately 12575 Hz, the signal-to-noise ratio of the output audio is improved, relative to the signal-to-noise ratio of the input audio. 
       FIG. 6B  also depicts the signal-to-noise ratio of the output audio at the time indicated by the cursor  620  as having a signal portion of −64 dB and a noise portion of −73 dB. Thus, the signal-to-noise ratio of the output audio is improved, relative to the signal-to-noise ratio of the input audio, with the signal intensity of the output audio changed by +3 dB relative to the input audio, and the noise intensity of the output audio changed by −3 dB relative to the input audio. 
     As used hereby, the term “example” means “serving as an example, instance, or illustration”. Any example described as an “example” is not necessarily to be construed as preferred or advantageous over other examples. Likewise, the term “examples” does not require all examples include the discussed feature, advantage, or mode of operation. Use of the terms “in one example,” “an example,” “in one feature,” and/or “a feature” in this specification does not necessarily refer to the same feature and/or example. Furthermore, a particular feature and/or structure can be combined with one or more other features and/or structures. Moreover, at least a portion of the apparatus described hereby can be configured to perform at least a portion of a method described hereby. 
     It should be noted the terms “connected,” “coupled,” and any variant thereof, mean any connection or coupling between elements, either direct or indirect, and can encompass a presence of an intermediate element between two elements which are “connected” or “coupled” together via the intermediate element. Coupling and connection between the elements can be physical, logical, or a combination thereof. Elements can be “connected” or “coupled” together, for example, by using one or more wires, cables, printed electrical connections, electromagnetic energy, and the like. The electromagnetic energy can have a wavelength at a radio frequency, a microwave frequency, a visible optical frequency, an invisible optical frequency, and the like, as practicable. These are several non-limiting and non-exhaustive examples. 
     The term “signal” can include any signal such as a data signal, an audio signal, a video signal, a multimedia signal, an analog signal, a digital signal, and the like. Information and signals described hereby can be represented using any of a variety of different technologies and techniques. For example, data, an instruction, a process step, a process block, a command, information, a signal, a bit, a symbol, and the like which are referred to hereby can be represented by a voltage, a current, an electromagnetic wave, a magnetic field, a magnetic particle, an optical field, an optical particle, and/or any practical combination thereof, depending at least in part on the particular application, at least in part on the desired design, at least in part on the corresponding technology, and/or at least in part on like factors. 
     A reference using a designation such as “first,” “second,” and so forth does not limit either the quantity or the order of those elements. Rather, these designations are used as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean only two elements can be employed, or the first element must necessarily precede the second element. Also, unless stated otherwise, a set of elements can comprise one or more elements. In addition, terminology of the form “at least one of: A, B, or C” or “one or more of A, B, or C” or “at least one of the group consisting of A, B, and C” used in the description or the claims can be interpreted as “A or B or C or any combination of these elements”. For example, this terminology can include A, or B, or C, or A and B, or A and C, or A and B and C, or 2A, or 2B, or 2C, and so on. 
     The terminology used hereby is for the purpose of describing particular examples only and is not intended to be limiting. As used hereby, the singular forms “a,” “an,” and “the” include the plural forms as well, unless the context clearly indicates otherwise. In other words, the singular portends the plural, where practicable. Further, the terms “comprises,” “comprising,” “includes,” and “including,” specify a presence of a feature, an integer, a step, a block, an operation, an element, a component, and the like, but do not necessarily preclude a presence or an addition of another feature, integer, step, block, operation, element, component, and the like. 
     Those of skill in the art will appreciate the example logical blocks, elements, modules, circuits, and steps described in the examples disclosed hereby can be implemented as electronic hardware, computer software, or combinations of both, as practicable. To clearly illustrate this interchangeability of hardware and software, example components, blocks, elements, modules, circuits, and steps have been described hereby generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on an overall system. Skilled artisans can implement the described functionality in different ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
     At least a portion of the methods, sequences, algorithms or a combination thereof which are described in connection with the examples disclosed hereby can be embodied directly in hardware, in instructions executed by a processor (e.g., a processor described hereby), or in a combination thereof. In an example, a processor includes multiple discrete hardware components. Instructions can reside in a non-transient storage medium (e.g., a memory device), such as a random-access memory (RAM), a flash memory, a read-only memory (ROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a register, a hard disk, a removable disk, a compact disc read-only memory (CD-ROM), any other form of storage medium, the like, or a combination thereof. An example storage medium (e.g., a memory device) can be coupled to the processor so the processor can read information from the storage medium, write information to the storage medium, or both. In an example, the storage medium can be integral with the processor. 
     Further, examples provided hereby are described in terms of sequences of actions to be performed by, for example, one or more elements of a computing device. The actions described hereby can be performed by a specific circuit (e.g., an application specific integrated circuit (ASIC)), by instructions being executed by one or more processors, or by a combination of both. Additionally, a sequence of actions described hereby can be entirely within any form of non-transitory computer-readable storage medium having stored thereby a corresponding set of computer instructions which, upon execution, cause an associated processor (such as a special-purpose processor) to perform at least a portion of a function described hereby. Additionally, a sequence of actions described hereby can be entirely within any form of non-transitory computer-readable storage medium having stored thereby a corresponding set of instructions which, upon execution, configure the processor to create specific logic circuits. Thus, examples may be in a number of different forms, all of which have been contemplated to be within the scope of the disclosure. In addition, for each of the examples described hereby, a corresponding electrical circuit of any such examples may be described hereby as, for example, “a logic circuit configured to” perform a described action. 
     In an example, when a general-purpose computer (e.g., a processor) is configured to perform at least a portion of a method described hereby, then the general-purpose computer becomes a special-purpose computer which is not generic and is not a general-purpose computer. In an example, loading a general-purpose computer with special programming can cause the general-purpose computer to be configured to perform at least a portion of a method described hereby. In an example, a combination of two or more related method steps disclosed hereby forms a sufficient algorithm. In an example, a sufficient algorithm constitutes special programming. In an example, special programming constitutes any software which can cause a computer (e.g., a general-purpose computer, a special-purpose computer, etc.) to be configured to perform one or more functions, features, steps algorithms, blocks, or a combination thereof, as disclosed hereby. 
     At least one example provided hereby can include a non-transitory (i.e., a non-transient) machine-readable medium and/or a non-transitory (i.e., a non-transient) computer-readable medium storing processor-executable instructions configured to cause a processor (e.g., a special-purpose processor) to transform the processor and any other cooperating devices into a machine (e.g., a special-purpose processor) configured to perform at least a part of a function described hereby, at least a part of a method described hereby, the like, or a combination thereof. Performing at least a part of a function described hereby can include initiating at least a part of a function described hereby, at least a part of a method described hereby, the like, or a combination thereof. In an example, execution of the stored instructions can transform a processor and any other cooperating devices into at least a part of an apparatus described hereby. A non-transitory (i.e., a non-transient) machine-readable medium specifically excludes a transitory propagating signal. Further, one or more examples can include a computer-readable medium embodying at least a part of a function described hereby, at least a part of a method described hereby, the like, or a combination thereof. A non-transitory (i.e., a non-transient) machine-readable medium specifically excludes a transitory propagating signal. 
     Nothing stated or depicted in this application is intended to dedicate any component, step, block, element, feature, object, benefit, advantage, or equivalent to the public, regardless of whether the component, step, block, element, feature, object, benefit, advantage, or the equivalent is recited in the claims. While this disclosure describes examples, changes and modifications can be made to the examples disclosed hereby without departing from the scope defined by the appended claims. A feature from any of the provided examples can be used in combination with one another feature from any of the provided examples in accordance with the general principles described hereby. The present disclosure is not intended to be limited to the specifically disclosed examples alone.