FXAlg #714: QFlange
Algorithm Reference-83
Clearly a one-bit word gives a very crude approximation to the original signal while four bits is beginning to do a
good job of reproducing the original decaying sine wave. When a good strong signal is being quantized (its word
length is being shortened), quantization usually sounds like additive noise. But notice that as the signal decays in
the above figures, fewer and fewer quantization levels are being exercised until, like the one bit example, there are
only two levels being toggled. With just two levels, your signal has become a square wave.
Controlling the bit level of the quantizer is done with the DynamRange (dynamic range) parameter. At 0 dB we are
at a one-bit word length. Every 6 dB adds approximately one bit, so at 144 dB, the word length is 24 bits. The
quantizer works by cutting the gain of the input signal, making the lowest bits fall off the end of the word. The signal
is then boosted back up so we can hear it. At very low DynamRange settings, the step from one bit level to the next
can become larger than the input signal. The signal can still make the quantizer toggle between bit level whenever
the signal crosses the zero signal level, but with the larger bit levels, the output will get louder and louder. The
Headroom parameter prevents this from happening. When the DynamRange parameter is lower than the
Headroom parameter, no more signal boost is added to counteract the cut used to quantize the signal. Find the
DynamRange level at which the output starts to get too loud, then set Headroom to that level. You can then change
the DynamRange value without worrying about changing the signal level. Headroom is a parameter that you set to
match your signal level, then leave it alone.
At very low DynamRange values, the quantization becomes very sensitive to dc offset. It affects where your signal
crosses the digital zero level. A dc offset adds a constant positive or negative level to the signal. By adding positive
dc offset, the signal will tend to quantize more often to a higher bit level than to a lower bit level. In extreme cases
(which is what weÕre looking for, after all), the quantized signal will sputter, as it is stuck at one level most of the
time, but occasionally toggles to another level.
A flanger with one LFO delay tap and one static delay tap follows the quantizer. See the section in this book on
multi-tap flangers (FXAlgs #154-155) for a detailed explanation of how the flanger works.
Block diagram of one channel of QFlange.
Quant W/D is a wet/dry control setting the relative amount of quantized (wet) and not quantized (dry) signals
being passed to the flanger. The Flange W/D parameter similarly controls the wet/dry mix of the flanger. The dry
signal for the flanger is the wet/dry mix output from the quantizer.
Parameters:
PAGE 1
In/Out
In or Out
Out Gain
Off, -79.0 to 24.0 dB
Quant W/D
0 to 100%
DynamRange
0 to 144 dB
Flange W/D
-100 to 100%
dc Offset
-79.0 to 0.0 dB
Headroom
0 to 144 dB
Input
Wet
Dry
Out Gain
Flanger
Dry
Wet
Output
Quantizer
