(FROM MANUAL)
■ Introduction.
The SD808 is Roland's TR-808 snare drum sound generator adapted for modular
synthesizer use. The front panel contains all of the controls found on the original TR-808
drum machine, allowing you full control over the snare drum timbres, volume levels to
mix with other drums, and accent levels. The module itself is very simple and
straightforward to operate; however, we highly encourage you to read this manual as it
contains useful information that will help you get much more out of the SD808. These
electronic drums are the heart and soul of our electronic music generation and learning
how to use them correctly will open up a world of organic analog beats and sounds for
you to utilize in your own music.
■About the Making of the SD808.
The SD808 is a one-to-one clone of the original circuit found in Roland's TR-808 drum
machine. The TR-808 was manufactured from 1980 till 1984, during this time Roland had
revised parts of the machine according to what they believed would make it either
sound better or electrically work better. One of the circuits that was
changed over time is the machine's white noise source: this noise source feeds di erent
sound generators and among them is the snare drum. The freedom of having a
dedicated noise source per each of our drum module allowed us to set it according to
what we found to sound better, and in the case of the SD808 we went with what Roland
thought to be an improvement and adapted the later noise circuit design.
When compared to several original machines we found a lot of variation, both in sound
clarity at different settings, length of the envelope, and timbre changes resulting from
different levels of accent. So is the SD808 sound like the original?
We believe so, the SD808 follows the original schematic and its representing math
precisely, down to the smallest details.
■Dynamics and Gain.
Accent and Levels:
Dynamic Accent and Level control of any drum sound in the mix is a big part of making
a beat sound right. Dynamic Accent provides emphasis on a particular not through
loudness. In analog circuits like the SD808, the accent pulse physically "hits" the
resonating circuit harder and the white noise VCA provides not only a louder sound but
also more attack and more noise to blend in (much like if you were to hit a real drum
harder or softer with a drum stick.)
While the original 808 has one global accent knob affecting all of its sounds
simultaneously, the SD808 (and all other drum modules in this series) offers an
independent accent level control. This feature adds far more dynamics than what was
possible with the original machine.
Accent Explained:
The accent input is a gate/trigger signal.
While the accent input is not in use, the incoming gate input is routed (normalized) to
both the accent input and the gate input. This serves for two purposes:
1. To allow you to reach the hottest drum sound possible even when there is no accent
input signal connected.
2. It makes the ACCENT knob act as a fine control of the output gain level. This is very
useful in situations where the level knob range is too coarse for setting precise levels in
a mix with other drum sounds.
■Connecting a gate signal into the accent input will break the internal routing mentioned
above and will allow for independent control over accent regardless of the incoming
gate signal. In this case as long as there is no accent signal present, the drum sound will
be set to the minimum accent level set internally, and once the accent input gets hit by
Tone explained.
The SD808 uses three sound generators to create the drum sounds, two of these
generators are the pure sine wave T-Network oscillators. Each of these oscillators
generate a sine wave that naturally decays over time. Each sine wave is set at di erent
pitch, one low, the other high. The TONE knob sets the mix of these two generators with
the low pitch sine at CCW, high pitch at CW and the mix of both in the full range sweep.
Snappy explained.
The SD808 white noise goes through a VCA that has its gain controlled by an envelope
generator. The SNAPPY knob controls the envelope generator amplitude but also has
a slight variation over the decay time. This either adds or subtract the white noise
component to the mix with the other two sine sounds. The amount of SNAPPY also
define how hard the Accent signal hitting this circuit will sound.
Great dynamics can be felt when playing the SD808 with accented and unaccented
notes with SNAPPY set just a tad higher then minimum.
Adjusting the noise source:
■Both the TR-808 and the SD808 comes with a trimmer that sets the gain of the White
noise generator. Your SD808 comes calibrated to factory setting according to the
original 808 calibration procedure. However, you are welcome to adjust it to your liking
by using the trimmer located on the left side of the module. Use a small flat-headed
screwdriver and experiment with different levels of noise.