Question about Linear Phase EQ versus Normal EQ versus Filter.
Let's say I want to modify the volume level (decrease it by 12 dB, say) of a single portion of the spectrum of a waveform while leaving the rest of the spectrum alone.
The way I understand these things is that due to the nature of waveforms being the compound of countless individual sine waves all summed together, it's impossible to alter the level of any one of those component sine waves without affecting all the other sine waves that make up the waveform.
So it seems like, when modify the volume level of a single portion of the spectrum, I can choose between two side-effects:
- Linear phase: Preserves the phase of component sine waves at the expense of altering the timing (noticeable on attack transients).
- Minimum phase: Preserve the timing of the waveform at the expense of altering the phase of the component sine waves (noticeable in phase-cancellation of stereo signals).
Here is the video I watched about this: EQ: Linear Phase vs Minimum Phase - YouTube
Assuming I'm right about the dilemma above, which of those two things—linear phase or attack transients—is preserved when using the following effects:
- Linear-phase EQ (I'm assuming this one is obvious)
- Normal multi-band EQ
- Filter
- Multiband compressor
Posted Feb 1, 2020, 6:34 AM UTC
Just to make sure we're on the same page:
Linear phase: Preserves the phase relationship between the individual sine waves of the signal but introduces a delay as well as pre-ringing and post-ringing.
Minimum phase: Does not preserve the phase relationship between the individual sine waves but does not introduce a delay (at least very very little) and has predominantly post-ringing.
This means that if you can't tolerate added latency (like in a live situation) or if the pre-ringing smears transients too much, you should go for the minimum phase EQ.
On to your questions:
Linear phase EQ: Uses linear phase filters
Normal multiband EQ: Unless otherwise specified, uses minimum phase filters
Filter: (assuming you mean something like a lowpass filter) Unless otherwise specified, uses minimum phase filters
Multiband compressor: Unless otherwise specified, uses minimum phase filters. Multiband compressors use special crossover filters that minimize phase cancellation when the individual bands are summed back together. When mimimum phase filters are used that basically results in an allpass filter, only altering the phase of the signal and balance of the frequency content (except for the gain difference the compression made).
This pretty much answers my question. I have another curiosity though:
Regarding your first two bullet points, it seems that all EQs and Filters introduce ringing when modifying a signal: So in regards to ringing (ignoring latency and phase), the only way they differ is in that Linear Phase introduces both pre- and post-ringing, whereas Minimum Phase introduces only post-ringing. Have I understood that correctly?
Also, regarding your last four bullet points: it seems that in regards to latency, phase, and ringing, there is no difference between a normal Multiband EQ, a Filter, and the Multiband Compressor. Is that correct?
Yes. I think, technically minimum phase filters also introduce a tiny, tiny bit of pre-ringing (2 samples or something) but don't quote me on that.
Yeah. You either have minimum phase (IIR) filters or linear phase (FIR) filters. You get more latency from lowpass/highpass/bandpass/bandstop filters which is also frequency dependent (longer filter for lower cutoff frequencies). Filters are filters, they operate on the same basic principle so they all have the same properties. A parametric EQ is realized using a biquad for minimum phase which requires a comparatively short FIR (linear phase) filter, which in turn means less pre-ringing and less latency. In contrast a lowpass filter will use multiple biquads which results in a longer impulse response so you'll also need a longer FIR filter. Again, this means more pre-ringing and more latency.
What about analog phase EQs?
Analog EQs are minimum phase as they are all IIR filters which are minimum phase by design.
Analogue EQs are uniformly minimum phase EQs. I don't think it would be practically possible to build an analogue linear phase EQ.