Phaser frequency effect

S

Sequence2

Member
Just reading my Access Virus synth Manual and once again I have no idea what the description for the Phaser frequency means

Phaser

Frequency (adjustable between 0 and 64)
-The characteristic corner frequency of the phasers all-pass filter. The frequencies of the left and right sides are shifted every so slighty to create a real stereo effect.

I assume it means that as I turn the knob clickwise (going from 0 towards 64) I get a more stereo effect from the phaser?

If anyone knows what is actually happening tho I would appreciate the feedback!
Thanks!
 
Sequence2 said:
Just reading my Access Virus synth Manual and once again I have no idea what the description for the Phaser frequency means
...
If anyone knows what is actually happening tho I would appreciate the feedback!
Thanks!
Click to expand...

I'm not that familiar with this particular synth and I've not looked at the manual, however, this is how the actual theory goes. A stereo effect can be simulated by having phase differences between the two channels. (Think of the phase shift as a very small time shift.) A phase shift can be created by using an "all-pass" filter. As the name implies, this filter lets all frequencies through (all frequencies that go in, come back out), but in doing so it introduces a phase difference. The wet and dry signals are normally mixed to give a phased effect. Anyway, for an all-pass filter the term cut-off or corner frequency is normally taken to mean the frequency at which the filter introduces -90 degrees phase shift of the input signal.

I hope this makes sense? I've tried to explain it without going into too much of the underlying theory.
 
Yeah I understand most of what you're saying I am just confused when you said:
"the frequency at which the filter introduces -90 degrees phase shift of the input signal."

So with the phaser frequency adjustment what is acutally happening as I increase the setting from 0 -> 127?
 
The amount of phase shift introduced by and all-pass filter is 0 - 180 degrees and is dependent on the frequency of the input signal. This is usually considered to be a linear (straight line) function, but this does depend on the implementation. So as the frequency of the audio signal (20Hz - 20KHz) increases the amount of phase shift increases i.e. for low frequencies (20Hz) there is 0 degrees phase shift (the signal is "in-phase" and reinforces the original) and for high frequencies (20KHz) there will be -180 degrees phase shift (the signal is completely "out-of-phase" and will cancel out with the original). A convenient point for engineers to define is the mid phase shift, -90 degrees. The exact frequency at which this occurs is called the corner frequency. On this synth you can obviously adjust the frequency at which the -90 degrees phase shift occurs. I don't know as I've not looked at this synth, but I would guess that a value of 64 on this control sets the corner frequency to around 10KHz (assuming linear operation). Then decreasing the value to 0 will move the corner frequency to a lower frequency. This would mean that the phasing effect would start occurring at lower frequencies. Equally increasing the value 127 would increase the corner frequency meaning the phasing effect will only be prominent at high frequencies. It is difficult to know the exact frequency values here as it would be dependent on the exact implementation of the filter and it is unlikely to have a pure linear operation.

Anyway, I hope you get the gist.
 
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