808 Tom Synthesis
The 808 features three conga/tom pairs (low, mid, and high), each sharing the same basic circuit design with differences in frequency, amplitude, and decay time. It has a bright, resonant attack that quickly transitions into a dull, non-resonant decay. This is achieved via a bridged-T oscillator whose frequency is forced down as the sound fades, creating a subtle downward pitch bend effect. This distinguishes them from the claves or cowbell which have a more ringing or pinging sound.
The tom is the same as the conga except for different tunings and the addition of some filtered noise.
Key Components:
• Each tom/conga pair has a bridged-T network based oscillator (low=IC15, mid=IC17, high=IC18) tuned to different frequencies for each part.
If you look at the circuit diagram you can see that each bridged-T is split in 2. When switched to tom, both halves are combined. When switched to conga one half is bypassed.
• Pink noise.
• An envelope generator (low=D55, mid=D57, high=D59).
• A VCA (low=Q52, mid=Q55, high=Q58).
808 Tom Tuning Guide:
High Tom (HT)
Frequency Range: Low = 165 Hz, Centre = 185 Hz, High = 220 Hz
Note Equivalents: Low = E3 +2 cents, Centre = F#3, High = A3
Decay Time: 100 ms
Mid Tom (MT)
Frequency Range: Low = 120 Hz, Centre = 135 Hz, High = 160 Hz
Note Equivalents: Low = B2 -49 cents, Centre = C#3 -45 cents, High = D#3 +49 cents
Decay Time: 130 ms
Low Tom (LT)
Frequency Range: Low = 80 Hz, Centre = 90 Hz, High = 100 Hz
Note Equivalents: Low = D#2 +49 cents, Centre = F#2 +47 cents, High = G2 +35 cents
Decay Time: 200 ms
Breakdown of the 808’s Tom Circuit:
1: The Body of the Sound:
Each conga/tom pair uses a bridged T-network based oscillator as a sound source. A bridged-T oscillator is an elegant circuit that combines a VCO, VCA, and ENV together using minimal components. Unlike standard oscillators that sustain indefinitely, the bridged-T design creates a self-dampening sine wave that rings briefly when triggered and naturally fades away, making it perfect for drum sounds.
2: Subtle Pitch Bend:
The bridged-T oscillator’s pulse is created by a feedback loop. As the feedback inside the bridged T-network dies down, two diodes (D80/D81 on the low, D82/D83 on the mid, and D84/D85 on the high) starve the circuit of electricity. These diodes' resistance increases as the sound fades, shortening the decay time and dampening the resonance, resulting in a subtle downward pitch sweep. This mimics how acoustic drums naturally change tone over time.
If you want to keep the sound authentic to the 808, don’t exaggerate the pitch bend. It should sound less like a boing, and more like a tonk.
Note: The low toms have a longer decay than the high toms.
3: Fake Reverb Effect:
Similar to the 808 clap, the tom creates an artificial reverb effect by adding a subtle amount of pink noise. The pink noise goes through a VCA and is shaped by an envelope with a slightly longer decay than the main body of the sound. This noise is quite subtle—many listeners may not notice it unless they deliberately increase the level—yet it contributes significantly to the tom's presence and dimensionality. When reproducing it, try filtering the noise down until it’s just on the edge of you starting to hear it. It should feel like a moment of extra air in the room.
Synthesizing an 808 Tom:
1: The Body of the Sound:
Use a sine oscillator: refer to the tuning guide above.
2: Filter:
Rout the oscillator through a filter. Use a band-pass, or notch filter.
Tune the filter to the same frequency as the oscillator.
Boost and accentuate the tuned frequency by using adding a mild to low amount of resonance.
Subtly modulate the filter frequency with a decay only envelope. The pitch drop shouldn’t be too immediately noticeable.
3: VCA & Envelope:
Pass the signal from the filter through a VCA or LPG.
Shape the VCA with a tight decay only envelope: 80 to 180 ms.
The initial attack should have a click.
6: Fake Reverb:
Start with pink noise.
The 808 Tom has a fairly dark pink noise, so you’ll have to filter it down. Pass the pink noise through a low-pass filter. Turn the frequency all the way down. Then raise it until you just start to hear the noise.
Pass the noise through a VCA. Shape the VCA with an envelope that’s a little longer than the one modulating the oscillator.
5: Optional Drive:
You can try adding a small amount of overdrive. Set the amount so the initial attack gets boosted and then has less effect on the tail. You don’t want the whole sound to get overdriven. The goal is to make only the attack brighter.
6: Variations:
Try sending velocity to filter resonance so louder notes will be brighter and lower velocity notes will be more clicky.
Control pitch with velocity.
Exaggerate the pitch drop. Increase the filter frequency’s envelope modulation.
Cascadia Patch:
See a Cascadia patch for the 808 Tom here.
Further Reading
Pg. 6 has a brief description of the combined tom/conga circuit (LT/LC (MT/MC, HT/HC)).
Pg. 7 has a block diagram (top right, between the SD and BD).
Pg. 9 the circuit (centre).
Pg. 14 has a chart displaying the frequency, and decay times (LT, MT, HT).
Erics Synths EDU DIY Kick Drum user manual.
For a good explanation of how a bridged-T oscillator works, check out Pg 9 through 12 of the user manual for the Erics Synths EDU DIY Kick Drum.