Classes (extension) | UGens > Generators

AY : UGen : AbstractFunction : Object

Emulator of the AY (aka YM) soundchip, used in Spectrum/Atari
Source: AY.sc


Emulates the General Instrument AY-3-8910 (a.k.a. the Yamaha YM2149) 3-voice sound chip, as found in the ZX Spectrum 128, the Atari ST, and various other home computers during the 1980s.

NOTE: The chip's inputs are integer values, so non-integer values will be rounded off.

The emulation is provided by the libayemu library: http://sourceforge.net/projects/libayemu - I have merely wrapped it up as a SC UGen.

Oscillator behavior

Typically, we think of oscillators as vibrating around zero (balanced output, with no DC offset).

The AY chip has three pulse oscillators and one noise oscillator (which may be multiplied in with the other oscillators' signals). They vibrate as follows (note that their sum is scaled down to valid floating-point signal range):

OscillatorLow valueHigh value
NOTE: There is always DC offset with this UGen. It's strongly recommended to use LeakDC on AY's output.

The control input controls whether the oscillator will be used or not, and whether the pulse wave will be multiplied by noise or not.

If control disables an oscillator, it produces its nonzero value as DC. This way, the three oscillators working together can access all 8 possible states resulting from three bits.

This means oscillator B will be perceived to be quieter than A, and C quieter than B.

This characteristic can be used to simulate wave shapes. For example, if A:B:C = fundamental : octave : 2 octaves, mixing the three oscillators at equal volume is close to a sawtooth wave.

Class Methods

AY.ar(tonea: 1777, toneb: 1666, tonec: 1555, noise: 1, control: 7, vola: 15, volb: 15, volc: 15, envfreq: 4, envstyle: 1, chiptype: 0, mul: 1, add: 0)



integer "tone" value for the first of the three voices, from 0 to 4095 (i.e. 12-bit range). Higher value = lower pitch. For convenience, the *freqtotone method converts a frequency value to something appropriate for the tone input.


integer "tone" value for the second of the three voices. See description of tonea.


integer "tone" value for the third of the three voices. See description of tonea.


the period of the pseudo-random noise generator, 0 to 31


controls how the noise is mixed into the tone(s), 0 to 63 (0 is mute). This is a binary mask value which masks the noise/tone mixture in each channel, so it's not linear.

Six bits are used: fedcba (with a being least significant and f most significant).

  • Bits a and d control oscillator A.
  • Bits b and e control oscillator B.
  • Bits c and f control oscillator C.
  • Bits a, b, and c turn oscillators A, B and C on or off, respectively: 001 = decimal 1 plays oscillator A only, 110 = decimal 6 plays oscillators B and C together. (Turning an oscillator "off" produces its nonzero DC value.)
  • Bits d, e and f multiply A, B and C respectively by noise. When the oscillator is "off" (nonzero), continuous noise is produced. When the oscillator is on, noise will turn on and off periodically according to the oscillator's frequency.

Control value 7 will mix A, B and C's clean tones together. Control value 0 reduces all oscillators to DC.


volume of the first of the three voices, 0 to 15 (or 0 to 31 if using YM chiptype).


volume of the second of the three voices, 0 to 15 (or 0 to 31 if using YM chiptype). Its perceived volume is 1/2 of oscillator A's volume.


volume of the third of the three voices, 0 to 15 (or 0 to 31 if using YM chiptype). Its perceived volume is 1/4 of oscillator A's volume.


envelope frequency, 0 to 4095


type of envelope used, 0 to 15


0 for AY (default), 1 for YM. The models behave slightly differently. This input cannot be modulated - its value is only handled at the moment the UGen starts.


general multiply controls for the resulting signal


general add controls for the resulting signal


converts a frequency value to something appropriate for the tonea, toneb and tonec inputs.

Inherited class methods

Instance Methods

Inherited instance methods