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The AY-3-8910 programmable sound generator, aside from normal 4-bit volume control, has a hardware volume envelope. This feature allows for defining the shape of the volume envelope at arbitrary speed according to 8 preset envelope shapes.

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Why Use Hardware Envelopes?

One may think, what is any upside of hardware envelope? Well, it’s somewhat independent of tone/noise generators, and since it goes so high in frequency, it can be used melodically! This guide explains how to make best use of the AY/SAA envelope.

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AY-3-8910 / AY8930

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Setup

In the instrument editor:
1

Configure Waveform Macro

Add a single tick to the “Waveform” macro with only envelope turned on. This will disable any output, but don’t worry.
2

Enable Envelope Macro

Add a single tick to the “Envelope” macro and select enable.
If you play a note now, you will hear a very high-pitched squeak. This is because you must set envelope period, which is the frequency at which the hardware envelope runs.

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Setting Envelope Period

You can set the envelope period in two ways:
  1. Manual control: Use 23xx and 24xx effects (envelope coarse and fine period)
  2. Auto-envelope: Use 29xx auto-envelope period effect and macros

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Auto-Envelope

Auto-envelope works via numerator and denominator:
  • Higher numerator = higher envelope pitch
  • Higher denominator = lower envelope pitch
Why are there both of these? Because the envelope generator might be used to mask the tone output (i.e., affect the square wave as well).
To mask the tone output, set the “Waveform” macro values to both tone and envelope. The higher the denominator value, the lower the envelope pitch relative to the square wave output, and similarly with the numerator. With the square-and-envelope setting, a lot of wild, detuned synth instruments can be made.

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Envelope Shapes

Depending on the “Envelope” macro value, different envelope shapes can be obtained:
  • Shape 8: The most basic one is a sawtooth wave
  • Direction: Inverts the envelope, producing the reverse sawtooth
  • Alternate: Produces an interesting pseudo-triangular wave, similar to halved sine. This can also be reversed
  • Hold: Disables the envelope
Pitch Resolution: The envelope pitch resolution is fairly low; at high pitches it will be detuned. Because of this, it’s used mostly for bass.
Single Generator: There is only one hardware envelope generator. You can’t use two pitches or two waveforms at once.

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SAA1099

SAA envelope works a bit differently from the AY envelope:
  • It doesn’t have its own pitch; instead, it relies on the channel 2/5 pitch
  • It has many more parameters than the AY envelope

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Setup

To use the SAA1099 envelope:
1

Configure Waveform Macro

Go to waveform macro and add a single tick set to 0 (unless you want to have a square wave mask).
2

Configure Envelope Macro

Set up an envelope macro. Turn on:
  • enabled
  • loop
  • Depending on the desired shape: cut and direction
  • Resolution will give you higher pitch range than on the AY
3

Place Notes

Place two notes in the pattern editor:
  • One in channel 2 will control the envelope pitch
  • The other in channel 3 can be any note you wish; it’s just to enable the envelope output

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Examples

Here are some examples of hardware envelope usage:

Demoscene-type Beat by Duccinator

Example of AY envelope in a demoscene-style track.

Philips SAA1099 Test by Duccinator

Demonstration of SAA1099 envelope capabilities.

Touhou Kaikidan: Mystic Square title theme by ZUN

Rare instance of AY envelope used for drums - it can be used to mask the noise generator output too.

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