Noise
BBD devices are noisy in comparison to other electronic devices. They hiss and the clock
signals that control the delay often sneak into the audio pathway. It is useful therefore to keep
the audio running through the module as high as possible but not high enough to cause audible
distortion – unless you actually like the distortion.
The Oakley Flanger does not use the noise reduction circuitry that some other devices use.
There are two types of noise reduction techniques typically used in BBD based flanger and
chorus units; pre-emphasis/de-emphasis and compression/expansion. Both types do indeed
reduce the overall level of hiss and grunge. But they also cause other sonic effects that in my
view detract from the sound. The best sounding analogue flangers in my opinion are the ones
that have no noise reduction circuitry.
That said, to reduce CV and clock breakthrough, the Oakley Flanger uses two flangers
running in parallel. Each flanger circuit, based around one MN3207 BBD, is controlled by the
same clock signal so the delay produced by each of them is identical. Also the audio signal
passing through each one is the same but with one important difference – one of them is the
inverse of the other. This is a differential audio signal and when one waveform is going up, the
other one is going down. If you were to add the two signals together then they would
completely cancel each other out. Here though, our two delayed, but out of phase, signals are
subtracted from each other. This reproduces the original signal at twice the size but also any
similar noise that both signals would have gained from going through the BBDs is cancelled
out. This technique is particularly effective at reducing CV breakthrough – where the CV that
controls the delay time sneaks into the audio path producing unwanted thumps and wheezes –
but it also improves signal quality too.
If you do find the level of noise objectionable in certain patches try using the flanger module
before your final VCA. This way the audio signal, including any added noise, from the flanger
will only be heard when the VCA is opened. The audio passing through the flanger will usually
drown out the relatively small amount of noise produced by the BBDs.
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