Process for high fidelity sound recording and reproduction of musical sound

A local performance simulation system simulates an ensemble sound pattern. The simulation system includes a signal generation system for simultaneously generating contact recording signals based on vibrations from the ensemble, where the ensemble produces an ensemble sound pattern. A signal processing system channelizes the contact recording signals and generates final instrument signals based on the channelized contact recording signals. The simulation system further includes a reproduction system with dedicated loudspeaker systems for generating audible sound waves based on the final instrument signals, where the sound waves simulate the ensemble sound pattern. Contact recording the vibrations and channelizing the contact recording signals eliminates all reverberation and reflection effects of the recording environment from the contact recording signals. Using a dedicated loudspeaker system for each instrument in the ensemble allows the simulation system to capture the reflection and reverberation effects of the listening environment, and creates the impression that the ensemble is present in the listening environment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to sound recording and reproduction systems. More particularly, the present invention relates to local performance simulation.

2. Discussion of the Related Art

Sound recording and reproduction has long been the subject of research, development and debate. Conventional stereophonic practices create a musical environment for the listener by including recording environment information, specifically early reflections and reverberation. Recording engineers therefore pay close attention to the recording hall and the location of the microphones when they record ensembles. When the original recording has inadequate environment information, such information is typically added artificially through electronic reverb boxes and ambience synthesizers. Artificial addition is essential when the original recording is made electronically or by tight-miking techniques.

The value of replacing recording environment effects with the actual effects of the listing environment, therefore, have largely gone overlooked. There are many circumstances, however, in which it is quite desirable to simulate a “local performance.” For example, there is a small but significant market of classical music connoisseurs who would greatly value the experience of a string quartet playing in the comfort of their own homes. Another benefit of local performance simulation is the possibility of elimination of intermodulation (IM) distortion between the tones of different instruments. Because the tones of a musical instrument tend to be harmonic, local performance simulation would limit distortion to harmonic distortion only, causing only a slight change in coloration for the instrument.

It is also desirable to provide the ability to highlight a particular musical instrument in an ensemble for educational purposes. Similarly, local performance simulation would allow the tone color of each instrument to be varied to taste. For instance, when listening to a simulated quartet, the listener could elect to give the second violin a darker tone color to exaggerate the difference between it and the first violin. There is also a need to individually shut off any instrument of the ensemble to provide a “music-minus-n” system. The local performance technique would allow the performer to feel that the other musicians of the ensemble are with her and around her, in the same listening environment. Furthermore, because each instrument would be recorded separately, editing of recordings and processing of individual voices would be facilitated. Errors by one musician could be corrected without the participation of the other musicians. It is also desirable to optimize loudspeakers for their particular functions. This would eliminate the present need, for example, for a large low-frequency driver (woofer) in the system that is dedicated to a flute. Dedicating loudspeaker systems would therefore control the cost of multi-channel ensembles.

Present stereophonic practice sometimes attempts to localize sound images, but localization is psychoacoustically fragile. This means that present audio imaging approaches depend on the loudspeakers, listening environment, and listener position used by the ultimate consumer. Adding to the difficulty is the fact that the principle function of stereo is to de-localize the sounds from the loudspeaker positions themselves and to provide a broadened image. In other words, stereophonic recording by definition attempts to bring the listener into the recording environment instead of bringing the musical performance into the listening environment. Furthermore, conventional stereophonic sound reproduction and contemporary surround sound techniques require the listener to be in a particular place or area. It is thus desirable to provide a sound recording and reproduction system with accurate imaging capability. This capability would allow the listener to perceive the individual instruments or voices to be spatially compact, and well-localized in azimuth, elevation and distance. Furthermore, it would be desirable to allow the listener to walk entirely around the synthesized performing ensemble.

SUMMARY OF THE INVENTION

In view of the above, a need exists for a system capable of accurately simulating the radiation pattern of each instrument in an ensemble. Accordingly, the present invention provides a method and system for simulating an ensemble sound pattern. The local performance simulation system includes a signal generation system for simultaneously generating contact recording signals based on vibrations from an ensemble, where the ensemble produces an audible ensemble sound pattern. A signal processing system channelizes the contact recording signals and generates final instrument signals based on the channelized contact recording signals. The simulation system further includes a reproduction system for generating audible sound waves based on the final instrument signals, where the sound waves simulate the ensemble sound pattern.

Thus, the method includes the steps of simultaneously generating contact recording signals based on vibrations from the ensemble, where the ensemble produces an audible ensemble sound pattern. The contact recording signals are channelized, and final instrument signals are generated based on the channelized contact recording signals. The method further provides for generating audible sound waves with a reproduction system based on the final instrument signals, where the sound waves simulate the ensemble sound pattern.

In another aspect of the invention, a method for tuning a local performance simulation system is provided. The tuning method includes the steps of matching a system overall frequency response to a known overall frequency response, and matching a system coarse asymmetrical frequency response to a known coarse asymmetrical frequency response. A system fine asymmetrical frequency response is further matched to a known fine asymmetrical frequency response. The system overall frequency response, system coarse asymmetrical frequency response and system fine asymmetrical frequency response simulate a frequency response of an audible ensemble sound pattern produced by an ensemble.

Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated inFIG. 1, a local performance simulation system20simulates an ensemble sound pattern by producing sound waves which simulate the ensemble sound pattern. The simulation system20has a signal generation system30, a signal processing system50, and a reproduction system70. The signal generation system30simultaneously generates contact recording signals based on vibrations from an ensemble21, where the ensemble21produces an audible ensemble sound pattern. The signal processing system50channelizes the contact recording signals and generates final instrument signals based on the channelized contact recording signals. The simulation system20further includes a reproduction system70for generating audible sound waves based on the final instrument signals, where the sound waves simulate the ensemble sound pattern. The reproduction system70therefore uses the reflection and reverberation effects of the listening environment to create the perception that the ensemble21is present and that the ensemble sound pattern is being generated from within the listening environment.

Preferably, the ensemble sound pattern emanates from a plurality of instruments, and as shown inFIG. 2, the preferred embodiment simulates a string quartet21′. It will be appreciated that while it is preferred to simulate a string quartet21′, other instruments such as brass or wind instruments can be simulated without parting from the spirit and scope of the invention. As shown inFIG. 3, the signal generation system30preferably includes a plurality of contact recording configurations31for converting the vibrations from ensemble21into contact recording signals.FIG. 4demonstrates that each contact recording configuration31preferably includes a pair of contact transducers coupled to a corresponding instrument22. The location of each contact transducer is governed by listening tests and cross-correlation function measurements in different frequency bands at different locations. Specifically, each pair of contact transducers includes a first transducer32located below an F-hole23of the corresponding instrument22. The first transducer32generates a contact recording signal based on vibrations near the F-hole23. A second to contact transducer33is located under a bridge24of the corresponding instrument22. Similarly, the second transducer33generates a contact recording signal based on vibrations near the bridge24. As will be discussed below, the signals from the transducers32,33are simultaneously recorded to separate channels using sound recording techniques well known in the art. Thus, two channels per instrument are created in the preferred embodiment.

Turning now toFIG. 5, the preferred signal processing system51is shown in greater detail. The signal processing system50includes a storage system51for storing the contact recording signals to a storage medium53as channelized data. A retrieval system52retrieves the channelized data from the storage medium53. It will be appreciated that storage medium53is preferably a computer readable medium such as a CD-ROM or DVD. As shown inFIG. 6, it is preferred that the storage system51include an analog to digital conversion system54for generating digital recording signals based on the contact recording signals from the signal generation system30. A recording system55generates the channelized data based on the digital recording signals and records the channelized data to the storage medium53. The signals are therefore maintained on separate channels throughout the simulation process. It will further be appreciated that as shown inFIG. 7, the retrieval system52of the signal processing system50preferably includes an equalization system56for tailoring a frequency response of the channelized data. A mixing system57generates intermediate instrument signals based on the channelized data. The preferred retrieval system52further includes a digital to analog conversion system58for generating final instrument signals based on the intermediate instrument signals. Thus, amplifier59can amplify the final instrument signals for transmission to the reproduction system70.

The reproduction system70will now be described in greater detail.FIG. 8demonstrates that the reproduction system70A includes a plurality of loudspeaker systems71,72,73and74. It is preferred that each loudspeaker system71,72,73and74has an assigned instrument and generates audible sound waves which approximate a frequency dependence of sound wave radiation from front, back and side surfaces of the assigned instrument. As best seen inFIG. 9, the reproduction system70may also include a means for simulating musician absorption of the audible sound waves such as absorption panel75. It can further be seen that each loudspeaker system includes at least one front driver76having a predetermined front piston diameter for approximating the frequency dependence of radiation from front and side surfaces of the assigned instrument.FIG. 9further demonstrates that a second front driver77can also be provided. Furthermore, as cost considerations permit, loudspeaker systems can have side drivers78,79to further increase accuracy of the simulation. As will be discussed later, each instrument has an asymmetrical frequency response. This asymmetrical frequency response is essentially an angular dependence of radiation from all surfaces of the instrument. Angular dependence can be matched in its coarse structure and approximated in its fine structure.

It will be appreciated that the simulation system20matches the simulation coarse angular dependence to a reference coarse angular dependence by two techniques. First, the frequency dependence of the radiation from front and back surfaces is approximated by using separate loudspeaker drivers. Thus, back driver80has a predetermined rear piston diameter for, approximating the frequency dependence of radiation from back and side surfaces of the assigned instrument. Furthermore, front drivers76,77reproduce radiation in the forward direction of the assigned instrument. The second matching technique approximates the polar radiation pattern. The polar pattern on radiation is approximated by using drivers with a piston diameter that reproduces the low-frequency lobe in the forward direction. For example, at an angle of 90 degrees the radiation from a viola is down 3 dB at a frequency of 1000 Hz. According to well-known theories for the radiation of a piston in an infinite baffle, a polar pattern with that characteristic requires a piston diameter of about 22 cm. The use of separate drivers76,77,78,79,80is further improved with the deployment of front and back equalizers (not shown) at the input to each driver76,77,78,79,80.

Turning now toFIG. 10, a method for tuning a local performance simulation system to the required frequency responses is shown in greater detail. Specifically, at step100, the system overall frequency response is matched to a known overall frequency response. The method further includes the step200of matching the system coarse asymmetrical frequency response and step300of approximating the system fine asymmetrical frequency response.FIG. 11shows step100in greater detail. It can be seen that at step101an instrument is selected from the ensemble. The musician then plays scales at step102, and contact and acoustic microphone recordings are simultaneously made at steps103and104, respectively. At step105, the equalizer is adjusted so that the overall frequency response of the simulation, measured in one-third-octave bands approximates the overall frequency response of the microphone recording.FIG. 14demonstrates that recordings are made with contact recording configurations31as usual and, using a separate recorder, with acoustical microphones25. In constructing the listening system, the loudspeakers are adjusted so that when they reproduce the signals from the contact transducers31, the long-term spectrum measured with the same acoustical microphones25and the same reverberant environment matches the original recordings. Perceptually important spectral structures in the real instruments will be captured by the third-octave matching technique.

As noted above, each instrument also has an asymmetrical frequency response which has an angular dependence. With respect to coarse structures, the overall directional frequency response of musical instruments has been measured in anechoic rooms by many workers. For example, Jurgen Meyer has measured the angular dependence of the frequency response for many orchestral instruments including the violin, viola and cello. These responses appear in his 1978 textbook entitled “Acoustics and the Performance of Music”.

Turning now toFIG. 12, the process of matching coarse asymmetrical frequency response is shown in greater detail. At step201, the instrument is selected and at step202, the reference coarse angular dependence is determined. The reproduction of the contact recording is matched to the reference at step203by the loudspeaker design techniques described above.

As shown inFIG. 13, the present invention also provides for matching the fine asymmetrical frequency response. The fine structure of the radiation pattern of a musical instrument is complicated. For violins, the fine structure is different from violin to violin. The result of the fine structure is that when the musician plays changing notes, the different high frequency harmonics are radiated in directions that change dramatically. This effect lends interest to the sound of the instrument and the tone is perceived as being more lively. The present invention does not attempt to reproduce the fine structure of any particular instrument. What is thought to be important is simply that some complicated fine structure be present. For each instrument of a stringed quartet, multiple loudspeakers can be used. Each speaker is driven by a weighted mixture of bridge and F-hole signals with possible inversion. The resulting interference pattern leads to the fine structure of the instrument. At this time, the weighting functions and decisions to invert are tuned by ear. Thus, at step301, the instrument is selected and at step302, the contact recording reproduction is matched by ear.

There are numerous alternative implementations of the present invention. For bowed string instruments, the individual radiation pattern can be simulated by comb filtering as in existing mono to stereo converters. In this case, it is adequate to record a single channel for each instrument and tight-miking might be used instead of contact pickups. For brass and woodwind instruments, the recordings can be made with mouthpiece pickups. After filtering, these recordings are reproduced through characteristic loudspeakers. Brass instruments use a single piston driver of appropriate size, whereas woodwind instruments require a more complicated design.

It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.