6
Signal Flow
DRIVE
CLIP
WAVE
WINDOW
WAVE
SHAPER
WAVE
FOLDER
S/H
LFO
BITS
FILTER
AMP
MIXER
IN
OUT
AGC
Bit crushing and waveshaping are amplitude-dependent effects, so it is helpful to be familiar with gain
staging. Gain staging is adjusting the signal level at each point in the signal path - usually to maximize
signal-to-noise ratio without distortion. In this case, we adjust the signal level to get different effects.
The
DRIVE control amplifies the input signal with hard clipping. Use it to adjust the input gain based
on signal level. The preset and wave LEDs display the signal level for a few seconds after the knob is
moved (the
⚠
LED indicates clipping). Lowering the drive will cause the signal to sputter and cut out.
Increasing drive will give a more saturated sound.
The wavefolder, wave window, or waveshaper can be used instead of sample rate modulation to create
additional nonlinear distortion. The
DEPTH knob adjusts the transfer function that is applied to the input
signal, adding more harmonics as you increase the depth. The effect is amplitude-dependent, so the
combination of
DRIVE and DEPTH settings give a wide range of possibilities. Using DRIVE to clip the in-
put signal will flatten the output at a level controlled by the
DEPTH (not necessarily the waveform peak).
After drive and waveshaping, the signal is sampled and bit-depth reduced. Samping rate reduction
(
FREQ) causes higher partials to fold back down to lower frequencies, where they intermix with the
lower partials, creating inharmonic distortion based on the relationship between the instrument's pitch
and the sampling rate. Bit reduction (
CRUSH) makes the waveform less accurate and adds noise that
is correlated with the signal - quiet when you are not playing, white noise during louder passages, and
static-y artifacts as notes decay. The Bitmap uses digital models of A/D and D/A converters similar to
early samplers, which adds additional nonlinearities.
After the sampling rate and bit-depth reduction, a 4-pole lowpass
FILTER can be used to smooth out the
rough edges. Resonance is available via MIDI, and you can modulate the filter cutoff by the LFO or enve-
lope for dynamic filtering.
An automatic gain control (AGC) block analyzes the input signal and the effected signal and tries to
match their loudness so that you can smoothly blend from dry to wet. We tried to handle this automat-
ically - without a separate output level knob - to avoid having to constantly tweaking the output level as
you adjust all of the other controls. (If you find a case where it does not work, please let us know.)
