CSC 320 – Music Instrument Digital Interface (MIDI) and Digital Audio, Spring 2017

1. CSC 320 – Music Instrument Digital Interface (MIDI) and Digital Audio, Spring 2017 April 2017 Dr. Dale Parson

2. Musical Instrument Digital Interface • MIDI stores, transmits, and receives information to control electronic musical instruments, including hardware and software synthesizers. • MIDI messages are packets of data, sent or received by a synthesizer or MIDI controller device. • MIDI is not Digital Audio. • Digital Audio is a sequence of binary numbers representing measurements of sound pressure levels (SPLs). • MIDI numbers do no represent sound. They represent control of instruments.

3. MIDI Short Messages • See javax.sound.midi.ShortMessage. • http://docs.oracle.com/javase/7/docs/api/index.html • See the MIDI specification. • http://midi.teragonaudio.com/ • See NOTE_ON to start a note, NOTE_OFF to stop it, PROGRAM_CHANGE to change the instrument voice, CONTROL_CHANGE for audio effects. • There are many distinct messages. • http://midi.teragonaudio.com/tech/midispec.htm

4. Chords & Instrument Voices • Polyphonic synthesizers can play many notes at a time. Monophonic synths play 1 at a time. • A MIDI channel 0..15 (1..16 on most user interfaces) represents one instrument. Thus a given synth supports addressing up to 16 simultaneous instruments, each of which may be polyphonic.

5. Program Change & Control Change • A Program Change message enables a channel to play a new instrument, 0..127. • Bank switching may support > 128 instruments. • A Control Change applies an effect to a channel in the amount 0..127 or 0..16383. • Not all synthesizers support all combinations of NOTE_ON ranges, Programs & Controllers.

6. Hardware & Soft Synths • A synthesizer may be a hardware device connected via a MIDI cable, or software connected to a controller via a soft bus. • There are 3+ basic approaches to synthesizing sound: • Harmonic synthesis combines overtones by adding or subtracting component sine waves. It models sounds. • Samplinguses recorded instrument sounds and pitch shifting as the basis for sound reproduction. • Physicalmodeling uses software that models the acoustic properties of physical instruments. • There are other, less heavily used approaches.

7. ConcentricCirclesIntervals • We will go over my ConcentricCirclesIntervals sketch, posted on the course page, that takes advantage of some of these additional MIDI features.

8. Pulse Code Modulation • PCM is a digital representation of Sound Pressure Level (SPL). It is the primary digital representation of audio signals (sound). • It is not instrument-control data like MIDI. • PCM converts a series of measurements of analog SPLs to a sequence of binary numbers, where the magnitude of a number represents the SPL strength during a brief interval of time.

9. http://www.electronicshub.org/modulation-and-different-types-of-modulation/http://www.electronicshub.org/modulation-and-different-types-of-modulation/

10. There are two categories of resolution in PCM. • Samples per second gives the rate at which PCM takes measurements of sounds. The lowest standard rate is 44,100 samples per second. • Bits per samples gives the resolution of each sample in terms of how many bits store each measurement. 16 bits per sample is a common minimal amount, giving numbers in the range 0..65536 or -32768..32767. Some old systems use 8-bit samples (0..255). 24-bit samples are common (0..16,777,215), • Sample rates go to 192,000 samples per second.

11. SoundToWavePixels • We will go over my SoundToWavePixels sketch, posted on the course page, that converts PCM-encoded audio signal data into pixel waveform displays. • This requires using polarized_shuffle.mp3. • Will will also go over PShape3DGroups, previously posted on the course page, that shows using a PImage as a PShape texture. • This requires using Window250x250.png.