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Topic: Do Digital Equalizers Cause Phase Shifts? (Read 22243 times) previous topic - next topic
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Do Digital Equalizers Cause Phase Shifts?

Reply #25 –
Quote from: rpp3po on
Is that true? I didn't know that, yet. Interesting!

But wouldn't a phase shift have to be applied into the opposite direction on the time axis? Or does "de-equalizing" and equalizing with two opposite minimum-phase filters* automatically restore the original phase instead of applying two (non canceling) shifts?


* For example, a Q6/+12db bell filter at 16 kHz and a Q6/-12db bell filter at 16 kHz.


Well, in the analog world nothing is ever exact, but if you have a highpass filter that has the exact opposite transfer function (i.e. inverse) of the lowpass, the two will (mathematically) cancel.
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J. D. (jj) Johnston

Do Digital Equalizers Cause Phase Shifts?

Reply #26 –
Quote from: rpp3po on
Is that true? I didn't know that, yet. Interesting!

But wouldn't a phase shift have to be applied into the opposite direction on the time axis? Or does "de-equalizing" and equalizing with two opposite minimum-phase filters* automatically restore the original phase instead of applying two (non canceling) shifts?


* For example, a Q6/+12db bell filter at 16 kHz and a Q6/-12db bell filter at 16 kHz.

If you draw scetches of the Z-transform, then it is actually quite intuitive.

The point is that "minimum-phase" sets some constraints on where you put your poles and zeros, namely that all poles and zeros have to be within the unit circle, meaning that its inverse is found by swapping poles and zeros, and both are guaranteed to be stable.

Now, the practical question is "what physical/natural systems are minimum-phase"?

-k
 

Do Digital Equalizers Cause Phase Shifts?

Reply #27 –
Quote from: knutinh on
Quote from: rpp3po on
Is that true? I didn't know that, yet. Interesting!

But wouldn't a phase shift have to be applied into the opposite direction on the time axis? Or does "de-equalizing" and equalizing with two opposite minimum-phase filters* automatically restore the original phase instead of applying two (non canceling) shifts?


* For example, a Q6/+12db bell filter at 16 kHz and a Q6/-12db bell filter at 16 kHz.

If you draw scetches of the Z-transform, then it is actually quite intuitive.

The point is that "minimum-phase" sets some constraints on where you put your poles and zeros, namely that all poles and zeros have to be within the unit circle, meaning that its inverse is found by swapping poles and zeros, and both are guaranteed to be stable.

Now, the practical question is "what physical/natural systems are minimum-phase"?

-k


Many less than one would wish for.
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J. D. (jj) Johnston