Abstract:
The invention disclosed is a system for playing a music sequence such as a MIDI file in synchronization with a prerecorded CD. The synchronization is accomplished by using the digital media sample rate as a common time base for progression of the playing of the digital media and the music sequence.

Description:
RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional application 60/713,936, which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to the area of automated musical instruments, particularly pianos, the invention also relates to the method of creating or authoring music sequences files for use with the automated musical instrument. 
   BACKGROUND OF THE INVENTION 
   Automated musical instruments, such as pianos, are well known in the art. Such instruments are typically acoustic instruments that use mechanical actuators to operate the instrument. The actuators receive commands of articulation events or music sequences to control or play the instrument. The music sequences are delivered to the instrument by a controller. There have been a number of attempts to have an automated instrument play in synchronization or accompaniment with a prerecorded CD or hard drive. Such attempts are described in U.S. Pat. Nos. 5,138,925, 5,300,725, 5,148,419 and 5,313,011. In order allow for synchronous play, those previous attempts rely upon timing information presented on a sub-channel of the CD to provide a common time frame for both the music sequences and the CD audio to reference. While such an arrangement is sufficient, it suffers from the limited resolution offered by the timing information of the CD sub-channel. The timing information of the CD sub-channel has a period or resolution of 13 milliseconds, which is not accurate enough for some piano sequences. The present invention described herein uses the timing inherent in the CD audio data as the time reference. By the use of this technique, the timing can have a period or resolution of 22.7 microseconds based upon the sample rate of 44.1 kHz of the digital audio data of the CD 
   While listening to the automated instrument playing alone is entertaining for the user, some users desire to have the instrument play along with a commercial recording of a musical selection, thus allowing the user to experience the recorded selection accompanied by a live automated instrument. 
   In early products for playing an automated piano in synchronism with a CD, the CD media contained music sequences that were pre-synchronized to a digital accompaniment music track encoded as linear PCM. For instance, the audio music track would be encoded as PCM on the left channel of the CD, and the music sequence, encoded as MIDI, would be encoded on the right channel. In the invention described herein, the system utilizes off the shelf commercially recorded CD, and music sequences specifically authored to play in synchronism with the musical selections on the CD. The music sequences are generally MIDI files stored on removable media such as SD cards and the like. One skilled in the art will recognize that there are many ways to deliver the music sequences, such as MIDI files, to the consumer and ultimately to the controller of the automated musical instrument, and SD cards are but one example. 
   SUMMARY OF THE INVENTION 
   The system described herein includes a controller for delivering the music sequences to the automated musical instrument. The controller is also in communication with a drive capable of playing digital media such as a CD. The controller, using the CD audio data as a time reference, delivers the music sequences to the automated musical instrument so that the instrument plays in synchronism with the selection playing on the CD. One skilled in the art will recognize that the controller could also host and act as the player for the music sequence with the appropriate software. 
   The following terms and definitions are used in this specification. The definitions included herein are to add meaning to terms and are not meant to limit or otherwise supplant meanings that are understood by those skilled in the art.
         MIDI—Acronym for Musical Instrument Digital Interface. MIDI is a music industry standard for digitally communicating musical instrument articulation events as a sequence of one or more bytes per event. The standard includes mechanical, electrical and byte signaling specifications.   MIDI Interface—A physical interface across which MIDI bytes are sent and/or received.   MIDI Event—A byte sequence that encodes a single musical instrument articulation event such as ‘key on’ or ‘sustain pedal depressed.’   MIDI Sequence—A chronological sequence of time-stamped MIDI events that encapsulates a performance of one or more musical instruments.   MIDI Sequencer—A device that plays a MIDI Sequence in real time for the purpose of reproducing a musical performance.   Standard MIDI File (SMF)—A music industry standard for storing and retrieving MIDI Sequences to and from a digital data file commonly referred to as MIDI file.   Pianomation—A system for translating MIDI events to electro-mechanical activity for the purpose of automating an acoustic piano, or other automated musical instrument.   Controller—An electronic device used to drive Pianomation with music sequences, such as MIDI Events from various media.   DVD—Acronym for the consumer electronics Digital Video Disc standard and media.   CD Player—A device, such as an optical drive, that is capable of playing a CD.   CD Player Subsystem—An electronic Subsystem used to play CDs such as an integrated CD player ASIC and related electronic components contained within a larger system such as a Controller.   Music Sequence—A term used in this application to generically refer to a chronological sequence of time-stamped digital musical instrument articulation events that encapsulates a performance of one or more musical instruments. This could be a SMF, a MIDI Sequence, or an otherwise encoded sequence that achieves the same objective.   Sync-Along CD—The technique described herein for synchronizing a music sequence to a CD Player or CD Player Subsystem.   Sync-Along CD Device—The device that implements the technique. This device can either attach to or be contained within a controller.   PCM—Acronym for Pulse Code Modulation. This term refers to the linear digital encoding of instantaneous audio amplitude at a constant sample rate. This is also referred to as uncompressed digital audio.       

   In the present invention, the controller, through use of a CD drive and subsystem incorporated into the controller, acts as both the MIDI Sequencer and the CD playback device, so the controller has inherent and immediate knowledge of what CD audio track is being played and what that track&#39;s time progress is authored music sequences to accompany commercial CD release. Typically, these commercial CDs will contain musical performances and the object is to drive the automated musical instrument synchronously along with the CD. 
   These pre-authored music sequences are synchronized to the digital audio stream of the CD per track. This means that a particular track is extracted from the CD by the authoring system. Once this is done, it is played by the authoring system which is simultaneously capturing a live piano performance along with it and converting that performance to a music sequence, typically in MIDI format. The time stamps use the CD&#39;s extracted digital audio stream as its source of time reference rather than some other system time. Hence, the resulting music sequence is synchronized to the CD track on any playback system as long as the playback system uses the CD&#39;s digital audio stream as its time reference. 
   Once the music sequence is authored or pre-authored as the process is alternatively named, it is associated with a CD song in some way. Since the Sync-Along device or controller is always the renderer of the CD Audio, it has specific knowledge of the CD that is being played, i.e., its Volume ID, and is always aware of exactly what track is being played. As such, the specific Volume ID and track number are stored as either Meta Events within the MIDI Sequence, or as part of the filename of the MIDI Sequence, allowing the controller to recognize what music sequence matches the CD being played. 
   Therefore, when a controller is instructed by the user to playback a particular track, the system loads the requested music sequence along with its Volume ID and associated track number and checks to make sure that that particular CD is loaded for playback. 
   Playback of audio CDs is implemented by the controller by reading the digital audio data, commonly referred to as Redbook audio data, directly off of the CD and sending that data to its DAC Subsystem for rendering to an analog signal. The DAC Subsystem itself is regulated by the audio rate of the DAC, which will nominally run at 44.1 kHz—the CD Audio sample rate. Hence, the data itself is consumed at the CD audio data rate by the DAC Subsystem which, via its DMA progress status, then provides the controller with an accurate digital audio time-base. 
   Once playback of the CD audio track has been initiated, the controller resets its internal sequencer time-base and monitors the progression of audio time as measured by the DAC Subsystem. As this digital audio time progresses, the controller submits the MIDI events to the Piano system in accordance with the event timestamps. Thus, the CD and the automated musical instrument are synchronized. 
   Since the automated Piano is a solenoid-actuated system, there is a measurable time delay from the time it receives a MIDI Event and the time it can actually sound a note on the automated acoustic Piano. In practice, his time can be as low as 100 ms or as high as 500 ms. Although the time is variable, the controller fixes the absolute delay from event reception to note sounding at 500 ms. Because of this delay, the controller advances the assertion of MIDI events during playback by 500 ms relative to the song start in order to maintain absolute synchronization to the CD as perceived by the user. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing the operational components of the system of the invention. 
       FIG. 2  is a front view of a controller. 
       FIG. 3  is a diagram showing the timely relationship between an analog audio output and a music sequence. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As shown in  FIG. 1 , the synchronization system  20  described herein includes a controller  22 , an automated musical instrument, such as a piano  24 , and an amplifier  26  and speaker  28 . The amplifier  26  and speaker  28  can be incorporated into the controller  22  in an alternate embodiment, and need not be separate devices. Similarly, the amplifier  26  and speaker  28  can be replaced with any combination of devices that will allow the user to hear the recorded material on the CD placed into the CD drive  40  of the controller  22 . Thus, it is beneficial for the housing of the controller  22  to include an audio output port for connection of the amplifier  26  and speaker  28 , or other device used to transduce the audio signal output from the controller  22 . In the preferred embodiment, the output port is a pair of RCA jacks  60  to allow play of the left and right audio channels of the CD, as shown in  FIG. 2 . 
   The controller  22  is connected to the automated musical instrument or piano  24  by a communication channel  35  capable of carrying the music sequences from the controller  22  to the piano  24 . In the preferred embodiment, the communication channel is a high speed UART serial channel. 
   The controller  22  includes a CD drive  40 , a digital to analog converter (DAC) subsystem  42 , a microprocessor  45 , random access memory (RAM)  47 , read only memory (ROM)  49  such as flash memory or an SD card or other removable media, a display  51 , and user controls  53 . 
   The CD drive  40  can be any optical drive capable of reading a CD meeting the redbook specification and outputting the digital music data and subchannels having information regarding the volume ID, track number and non-music data regarding the CD. The CD drive  40  shares a communications channel  54  with the microprocessor  45  to convey information regarding the CD to the microprocessor  45 , and to receive control commands from the microprocessor  45 . The CD drive  40  also shares a communications channel  56  with the DAC subsystem  42 . The communications channel  56  serves to send the digital audio data from the CD drive to the DAC subsystem  42 . 
   The DAC subsystem  42  of the preferred embodiment processes the digital audio data and converts the digital information into an analog signal. In the preferred embodiment, the DAC subsystem has two main parts, one of which may be incorporated into the microprocessor  45 . The first part is a DMA controller. The DMA controller moves audio data from the processor&#39;s RAM  47  to the DAC without processor intervention, as one skilled in the art will recognize In the preferred embodiment, the DMA controller is built into the TriMedia microprocessor. The DAC subsystem  42  also includes a digital to analog converter. In the preferred embodiment, the digital to analog converter is model CS4226 manufactured by Cirrus Logic. The DAC subsystem communicates with the microprocessor  45  by communications channel  55 . The communications channel is used to send information to the microprocessor  45 , access RAM  47  in communication with the microprocessor  45 , and to receive control commands from the microprocessor  45 . Among the information shared with the microprocessor  45  is the DMA progress status, or information regarding how many units of the digital audio data have been processed or output by the DAC subsystem  42 . The DAC subsystem  42  outputs the analog signal to the amplifier  26  by communications channel  56 . Communication channel  56  may include an output port  60  in the housing of the controller  22 . In the preferred embodiment, the output port is a pair of RCA jacks. 
   The microprocessor  45  is in communication with RAM  47  by communication channel  60 . In the preferred embodiment, the controller  22  has 1 gigabyte of RAM, although other amounts can be used. The microprocessor  45  is also in communication with ROM  49  by communications channel  61 . The ROM  45  is used to provide the music sequences, preferably MIDI files, to the controller  45 . In the preferred embodiment, the ROM  49  is an SD card. The controller  22  is provided with a slot or interface  48  that will accept the SD card and link the card to the communications channel  61 . On skilled in the art will recognize that other types of memory could be used for ROM  49 , provided the controller  22  has the appropriate interface and the microprocessor  45  has the corresponding inputs and software to accommodate the type of memory used. 
   In the preferred embodiment, the microprocessor is a TriMedia manufactured by Philips. Other microprocessors can be used to accomplish the tasks described herein. For example, the microprocessor should be able to feed data to the DAC subsystem, monitor the data progress, and interface with the CD drive to read raw audio data if desired. 
   The controller  22  includes a display  51  in communication with the microprocessor by communication channel  64 . The display is preferably an alpha numeric display capable of displaying information regarding the CD being played, as well as the music sequences available in ROM  49 . In the preferred embodiment the display  51  is a multi character fluorescent display. Other displays may be used to convey information to the user. 
   The controller also includes user controls  53  in communication with the micro processor  45  by communication channel  67 . In the preferred embodiment, the user control  53  includes a knob that can be rotated to scroll through the available selections, and pressed to select the displayed selection, which determines the music sequence the controller  22  will play. One skilled in the art will recognize that the user controls  53  can be any type of device that allows the user to interact with the controller  22 . For instance the user controls  53  could be a push button, keyboard, or touch screen. In the preferred embodiment, the display shows the titles of the music sequences available for play by the controller. The number of titles displayed at any one time depends upon the size of the display used. The user manipulates user controls  53  to change the titles displayed until the desired title is displayed and selected for play. 
   The titles are obtained from the files stored in ROM  49 . In the preferred embodiment, the ROM  49  contains music sequences corresponding to a particular commercial CD. The individual music sequences generally correspond to the tracks present on the commercial CD. The volume ID for the CD, and the track number are preferably stored as meta events in the music sequence. Alternately, the Volume ID and track number can form part of the file name for the music sequence file. The ROM  49  may also include a file to associate the song titles of the music sequence with the volume ID and track numbers of the CD. Thus, the controller  22  can display the song titles on the display  51  corresponding to the music sequences available in ROM  49 . 
   The music sequences are authored to the CD using standard authoring software such as a Digital Performer sold by Motu. During the authoring process, which is familiar to those skilled in the art, the music sequence is stored in a file as articulation or MIDI events. The timing or reference of the articulation events is based upon the audio rate or sample rate of the CD.  FIG. 2  shows the relationship between an analog audio signal  70 , such as the audio output of the DAC subsystem, and the articulation events  71  of a corresponding music sequence  72 . One skilled in the art will recognize that the analog signal  70  is created from the conversion of the digital audio data having a sample rate of 44.1 kHz, and that the authoring software relates the meta events to the timing of the digital audio data. Thus, when the CD is played in the CD drive  40 , the microprocessor  45  can access the DAC subsystem  42  to determine how many samples have passed since the beginning of play to obtain an accurate time base. Having that information, the microprocessor  45  can send the articulation event to the piano  24  at the correct time. 
   In the preferred embodiment, the piano  24  is a solenoid actuated system, and as such has an inherent delay between the time it receives a meta event and the sounding of the note on the piano  24 . In order to account for this delay, the microprocessor  45  sends the meta event to the piano  24  at a discrete time in advance of the timestamp of the meta event. In the preferred embodiment, the discrete time is 500 ms. Thus, the microprocessor  45  sends the midi event to the piano 500 ms earlier than called for by the timestamp associated with the event in order to achieve playing of the piano  24  in absolute synchronization with the CD. 
   In operation, the system  20  generally operates as outlined herein. One skilled in the art will recognize that the operation may vary depending upon the particular embodiment. The user selects a ROM device, such as a CD card, containing the music sequence files authored for a particular CD. The user inserts the ROM device into the slot or interface  48  on the face of the controller  22 , allowing the microprocessor  45  to access the files on the ROM device. The user also places the desired CD into the CD drive  40 . The microprocessor accesses the files on the ROM  49  and displays the titles of music selections available on the display  51 . The titles are displayed one at a time. In order to advance to the next available title, the user manipulates a user control  53 , which in the preferred embodiment is a rotatable knob. Rotation of the knob scrolls through the available music selections. 
   When the desired music selection appears on the display  51 , the user manipulates a user control  53  to start play, which in this embodiment involves pressing the knob. One skilled in the art will recognize that other types of controls or interfaces can be used. In response, the microprocessor  45  accesses ROM  49  and loads the selected music sequence along with its volume ID and track number in to RAM  47 . The microprocessor  45  then quires the CD drive to obtain the volume ID of the CD in the drive to determine if the volume ID of the CD in the CD drive  40  matches the volume ID loaded into RAM  47 . If the volume ID does not match, the microprocessor displays on the display  51  indicia such as “insert CD” or other instructions to the user to indicate that the CD in the CD drive  40  does not match the CD for the ROM device selected. If the volume ID does match, play of the CD audio data can begin. 
   To play the digital audio data, the microprocessor  45  resets an internal time sequencer and instructs the CD drive  40  to send the digital audio data to the DAC subsystem  42 . The DAC subsystem  42  converts the digital audio data to an analog signal, which is then output to an amplifier  26  for play on speaker  28 . The DAC also provides the microprocessor  45  with the time progress of the digital audio data processed by sending the microprocessor  45  timing information from the DAC subsystem&#39;s  42  DMA progress status. Monitoring this information, the microprocessor  45  knows what time it is relative to the start of the playing of the CD audio data. The microprocessor advances this time by a discrete amount, preferably 500 ms and tracks the time in its internal time sequencer. As the time in the internal time sequencer progresses, the microprocessor issues meta events to the piano  24  via communications channel  35 , thus allowing play of the piano in absolute synchronization with the CD being played. 
   The embodiments described herein are mere examples of the teachings of the invention. As such, they are not intended to limit the scope of the claimed invention.