Music – Instruments – Electrical musical tone generation
Patent
1996-10-28
1998-03-31
Wysocki, Jonathan
Music
Instruments
Electrical musical tone generation
84604, 84623, 84649, G10H 700
Patent
active
057341184
DESCRIPTION:
BRIEF SUMMARY
The invention relates to MIDI (Musical Instrument Digital Interface) playback systems.
TECHNICAL FIELD
MIDI is an internationally recognised specification for data communication between digital electronic musical instruments and other devices, such as computers, lighting controllers, mixers or the like. The MIDI data specifies performance information, as opposed to sound information. For example, which note or notes are being held down, if any additional pressure is applied to the note after being struck, when the key is released and any other adjustments made to the settings of the instrument.
MIDI data is communicated as a serial data stream over cables with standardised connectors at a standard baud rate. The digital data is organised into MIDI `messages`, which contain one MIDI command or event. MIDI commands are usually composed of one, two, or three bytes of data arranged and transmitted one after another. The first byte sent in each command is called the `status` byte and specifies an operation to be performed. The next one or two bytes, if used, represent parameters of this command. For example, a NOTE ON command comprises three bytes, the first of which is the status byte. This byte tells a synthesizer to play a note and specifies the channel number. The channel number usually represents the type of sound to be played, ie which instrument of the synthesizer is to be used. The second byte specifies the note to be played and the third byte specifies the velocity value for the note.
The bytes of the MIDI commands are specified in the MIDI standard. Part of this standard is a protocol which specifies that the leftmost bit of the status byte is always 1 and in all the following data bytes the leftmost bit is 0. In this way in a stream of MIDI data, the receiving device can always tell, if the leftmost bit in a byte is 1, that the byte is a status byte representing a new command to be processed. By decoding the status byte, the device can tell how many data bytes should follow the status byte.
In a conventional MIDI playback system a synthesizer, which is usually a special piece of hardware for generating sound data from the performance data, usually in the form of digital audio samples, is controlled by a MIDI sequencer in the following way. A standard MIDI file (SMF) contains a set of events, which are intended to be executed by a synthesizer at particular times. Generally, the events are not uniformly spaced in time. A conventional MIDI sequencer parses the standard MIDI file, reads the present MIDI event and the time difference between it and the next event. The sequencer then sends the event in a MIDI message to a MIDI synthesizer at the time it is to be executed. The sequencer usually sets a timer and reads the next MIDI event after this time difference has elapsed.
A conventional MIDI synthesizer receives the MIDI message that the sequencer sends, decodes the message and operates accordingly. For example, a `NOTE ON` event will cause the synthesizer to generate audio samples that correspond to a requested note and velocity that are supplied as parameters. Similarly, a `NOTE OFF` event will cause the synthesizer to cease generating the audio samples.
MIDI sequencers for MIDI playback systems usually use timing resolutions of less than 1 mS. This resolution is, to some extent, limited by the fact that baud rate at which MIDI data is communicated is 31,250 bits per second and there are 10 bits of data per MIDI byte (8 data bits+2 bits for error checking). Therefore, MIDI data can only be transmitted at around 3 bytes of data per mS.
However, this resolution is relatively high in comparison with the real time capabilities of currently available computer systems. Therefore, a software implementation of a MIDI sequencer consumes a large amount of host processing power as a result of context switching and high speed interrupts used to perform real time processing at this resolution.
It is known for MIDI sequencers to group events together in various ways into larger time intervals and send the events
REFERENCES:
patent: 5119711 (1992-06-01), Bell et al.
patent: 5300725 (1994-04-01), Manabe
Ashour Gal
Lisle Ronald Jay
Sharir Naftaly
Emile Volel
Fletcher Marlon Torriano
International Business Machines - Corporation
Wysocki Jonathan
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