WHY LINEAR-PHASE EQ SOUNDS MORE TRANSPARENT

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janpetter
Posts: 45
Joined: Sat Feb 05, 2005 7:00 pm

WHY LINEAR-PHASE EQ SOUNDS MORE TRANSPARENT

Post by janpetter »

Hi folks , I came over this interesting article .

http://emusician.com/tutorials/square-one-phase/

I was wondering as to the Filter Topology option in Har-Bal on when or what you guys used the linear phase option : - )

All the best
Jan
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Re: WHY LINEAR-PHASE EQ SOUNDS MORE TRANSPARENT

Post by HarBal »

Quoted from the article:

"Linear-phase EQs preserve the characteristic shape of a waveform by shifting all frequencies by the same amount"

Well, this is a dramatic over-simplification in as much as any filtering that does not alter the shape of the waveform at all is all pass (ie. effectively no filtering). Once there is a modification in the spectrum there is always a change in the waveform irrespective of linear or minimum phase responses.

Linear phase filters actually have longer impulse responses than equivalent minimum phase realisations so the argument that linear phase has less effect on transients is, to my mind incorrect. Linear phase filtering has far more importance in the area of digital communication systems where linear phase is important to help minimise inter-symbol interference.

In the audio world its justification in EQ work is somewhat dubious. The pre-echo of linear phase responses is audible and has an un-natural sound. Indeed, so it should because every natural process is far closer to minimum phase than linear phase. Linear phase does not occur in nature. As a result we aren't accustomed to hearing transients with pre-echo so when we do it sounds odd.

I can certainly hear the audible difference between linear phase and minimum phase filter realisations in har-bal and my ear definitely prefers minimum phase. That is essentially why it is the default but those convinced of linear phase superiority can still use it. All they need do is change the setting in "Equalizer Options" dialog box.

The only application where I think linear phase filtering makes a lot of sense in the audio world is in active crossovers for loudspeaker and PA systems. In that application the pre-echo issue does not come into play because the outputs from the separate drivers sum together in such a way that the pre-echo largely cancels out. I wouldn't use it in EQ applications and by and large, you can safely say that most mastering professionals don't by virtue of them using analog gear (aka Manley Massive Passive or something similar).

regards,


Paavo.
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