808 Clap Synthesis
The following is an outline for recreating the TR-808 Clap.
Ingredients of the 808 Hand Clap Circuit:
• White Noise
• Band-pass Filter, tuned to 1,000 Hz / B5 +21¢
• A ‘Sawtooth’ Envelope (Built Out of a Quad Comparator) = 50 ms
• A decay only ‘Reverb’ Envelope = 100 ms
• 2 VCAs
1 Sound Source:
Start with a white noise source. White noise contains all audible frequencies at equal intensity, similar to static hiss from a radio tuned between stations.
2 Filtering:
The white noise passes through a band-pass filter tuned to 1,000 Hz. This filtered noise is the basic texture of the clap. Experiment with different tunings and flavours of noise.
The filtered noise is sent to two VCAs in parallel paths. Path 1: A VCA modulated by a unique ‘Sawtooth’ envelope. This is the attack portion of the sound. Path 2: A VCA modulated by a longer ‘Reverb’ envelope. This is the tail of the sound.
3A: The sawtooth envelope:
A sharp percussive envelope that creates the clap’s snap. It is generated by four envelopes in rapid succession, simulating the crack of multiple hands clapping together. This is the main component of the clap sound, and creates its sharp, snappy character.
A 30 ms pulse is generated whenever the clap receives a trigger. This initiates a complex chain of charging and discharging that lasts for the 30 ms period. Each cycle lasts 10 ms. Each discharge produces a sawtooth shaped envelope. This produces 3 super fast envelopes. After, there’s a final uninterrupted discharge lasting 20 ms.
The envelope is mixed with the accent level, then applied to a VCA.
This process is explained on page 6 of the 808 Service Manual. For a detailed description of the envelope’s shaping process, see the diagram below, copied from the service manual.
3B The Reverb Envelope:
Not a reverb. This is an envelope with a smooth, relatively long (100 ms) decay. The fading noise is intended to create a fake, reverb-like effect, simulating the way a real hand clap rings out after the initial snap of the clap.
4 Mixing:
The parallel paths are mixed together.
Notes:
For snappier claps, turn the reverb path down in the mixer, or shorten its decay time.
Further Reading
Pg. 6 has a brief description of the clap circuit (CP / MA).
Pg. 6 there is a chart showing the voltage being shaped into the ‘sawtooth’ envelope.
Pg. 7 has a block diagram (top centre).
Pg. 9 the circuit (lower left).
Pg. 14 has a chart displaying the amplitude, and decay time.