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Page 573 ï~~CREATION OF MIDI FILES FOR ACOUSTICAL EXPERIMENT USING THE TX81Z Alain Pitre Engineer, M.Sc.A. Universite de Montreal 64 Fairmount W., #4 Montreal, PQ Canada, H2T 2M2 A sofware has been developed for use by experimental psychologists doing music perception research. This demonstration will show all the steps needed to build a single MIDI file for experiment. This file contains voices and scale tables for the TX81Z, specified with international units, and sequencial musical events. The software is built around an IBM-PC/AT compatible using an MPU-401 card to interface with the multitimbral synthesizer TX81Z from Yahama. The problem with a commercial synthesizer like this one is that the creation of sound is done by relative parameters (1 to 99) that have no trivial relation with real units. To be able to use such a synthesizer for experimental research the firmware and hardware of the TX81Z have been analyzed by "reverse engineering" the device. The software developed presents these derived values so that sound creation can be done with real units. The demonstration will start by creation of sound files and scale tables based on real units. The real unit interface is provided in addition to the "MIDI System Exclusive" code values. On the TX81Z a PERFORMANCE contains the parameter values for describing a complex sound. A PERFORMANCE is a combinaison of up to eight VOICES. Each VOICE is built with up to four oscillators. An oscillator contains one of the eight available waveforms, the basic one being a sine wave. Yamaha provides eight "algorithms" for connecting these oscillators. These connections are done by additive synthesis or/and frequency modulation. Each oscillator frequency can be fixed (specified in Hertz) or relative (ratio), the basic value being the pitch of the note. The amplitude of an oscillator can be specified in Decibel or relative (ratio) to its maximum value. An envelope, specified by its attack, decay and release values, is associated with each oscillator. These values are set in second and DB/sec. A Low Frequency Oscillator (LFO) is ICMC 573
Page 574 ï~~also available to modulate the pitch (Cents) or the amplitude (DB or ratio) of an oscillator at different speeds (Seconds). Beside predefined scales, two custom scale tables are available, one on a single scale range and the other one for the full keyboard. They can be specified in pitch value or in Hertz. The resulting file contains "System Exclusive" MIDI codes to setup the TX81Z. The sequential musical events are created by the PERSONAL COMPOSER software. In an experiment, hundreds of these sequences, composed of few notes, can be used. They are saved as graphical files called PC files. The menu driven program developed, called PASTE, compiles the PC files, each associated with specified parameters (tempo,channel,...) and keeps them as MIDI event files. Each MIDI event file and TX81Z MIDI file is associated with a symbol. The final sequence is described as a combination of symbols. The PASTE program takes each MIDI file associated with these symbols and pastes them together to give the final MIDI file used for an experiment. The PASTE program can play and analyze intermediate MIDI file results for debugging purpose. It also contains macro facilities to build demonstrations like the ones we will use. Several software tools have been developed to compile, play, analyze files from DOS. The PASTE program is presently used in the psychomusicology laboratory of Universite de Montreal where research works are done on musical perception. It has been developed with the feedback of the users working with previous versions for few years. The demonstration will create a single MIDI file containing the TX81Z sound configuration parameters, custom scale tables, and musical events. These events will contain different musical sequences played at different speeds, with different scales and voices, in some random order. Along with his studies at "Ecole Polytechnique de Montreal", Alain Pitre has obtained a First Prize in clarinet from the "Conservatoire de Musique du Quebec". He is presently working as a digital hardware engineer at "Image and Audio Systems". This company develops custom boards built with "DSPs" for audio applications. ICMC 574
Page 575 ï~~File Tx8lz Associate Compile Play paRameters Options Macro Info ASSOCI source Score # n A: M B: MN C: MN D: MN E: MN F: MN G: MN H: MN Voic A B C D E e Name Structure Envelope Amplitude Pitch Efem Toms taff up hannel Channel 1 vel accent bytes hr:mn:sc:ms A-f2 Ith" A Frequency Choice <4> Fix 240 Hz B Range <FFR> 0 <FRR> 3 C Coarse <CRS> 60 <FC> 15 D Fine <FF> 0 E Detune note C3 F det 0 <DET> 3 373 m Hz G Breath Ctl P Bias bc 0 BCPB" 0 0 Cent H Pitch Bend pb 64 PBR" 7 0 I Transpose C3 TRANS" G#3 I J K L M MN'L MNV10 MNV 11 MNVI2 MNV13 MV2 MV3 MV4 MV5 MVl7 MV19 MV21 MNV53 w x y z MV3 6 MV3 7 MV38 MV38 Figure 1: Screen display from PASTE for pitch setup in a voice File Tx8lz Associate Compile Play paRameters Options Macro Info EDIT SEQUENCE byt delay 12000 BEEP: number 0 duration 0 AH g ecu G yR LEt d K o v b PQmY IONhn Dx SCORE - A B C D E F staff <1 up> G channel <1> H I Synchro* TX81Z - J K SEQUENCE L M Beep N Mem unprotect Source Score Tempo 150 Ratio 7/8 Cut off 1 Delay* 1000 Channel 0 Velocity 0 Accent* 0 Duration 0 Synthe 1 Delay 12000 On MEMORY PROTECTION &M - A Duration 250 B Synthe <1> Protect Figure 2: Screen display from PASTE for parameters setup ICMC 575