mjfe2
Joined: 11/10/09
Posts: 504
Loc: Cambridge, UK
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normal EQ vs linear phase EQ
#994479 - 24/06/12 12:54 PM
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I read a lot about how many things 'should' sound without having the luxury of hearing
these things for myself. One thing I've been wondering about recently is how to listen
for phasing caused by a conventional EQ (e.g. ReaEQ, which I use in Reaper all the time).
Would I hear these problems by themselves without a linear phase EQ for comparison?
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C.LYDE
member
Joined: 22/10/02
Posts: 209
Loc: South Africa
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Re: normal EQ vs linear phase EQ
[Re: mjfe2]
#997717 - 13/07/12 05:20 PM
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Good question - applies to quite a few effect discussions, ... Emperors clothes ...  personally
I'm of the opinion if I can't hear the difference, its not worth breaking my head (or the
$$$). However putting on my scientific cap - use of a spectral type display - I
use Steinberg's Wavelab for detailed analysis, might be more helpful at revealing the
effects of phase interference ...
-------------------- C.LYDE
http://soundcloud.com/c-lyde
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Jack Ruston
Joined: 21/12/05
Posts: 4066
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Re: normal EQ vs linear phase EQ
[Re: mjfe2]
#997721 - 13/07/12 05:25 PM
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For me it's more when you're dealing with multi mic'd sources like drums, and you have a
good cogerant phase relationship at tracking, but after applying a lot of eq the sound
seems to collapse a bit power-wise. J
-------------------- www.jackruston.com
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mjfe2
Joined: 11/10/09
Posts: 504
Loc: Cambridge, UK
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Re: normal EQ vs linear phase EQ
[Re: mjfe2]
#1038174 - 14/03/13 02:45 PM
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Hmm, just wanted to re-open this discussion because I'm still not sure I understand how
EQs put the signal out of phase. If you EQ a single channel can its phase be affected?
Or does this only occur when multiple EQ bands are used? Or is it only made apparent on
multi-mic'd instruments where one channel is EQ'd, which sounds 'phasey' against the
non-EQ'd channel? Thanks in advance!
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Richie Royale
Joined: 12/09/06
Posts: 3369
Loc: Bristol, England.
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Re: normal EQ vs linear phase EQ
[Re: mjfe2]
#1038186 - 14/03/13 03:18 PM
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alexis
Joined: 10/01/03
Posts: 1204
Loc: San Antonio, TX USA
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Re: normal EQ vs linear phase EQ
[Re: mjfe2]
#1038199 - 14/03/13 04:05 PM
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Had been wondering if I should get a linear phase EQ for use in parallel processes (to
avoid "smearing"?), but have laid off because of 1) some talk about "pre-ringing" (??), 2)
descriptions that they are quite CPU intensive.
--------------------
Alexis -Cubase 6.5.0/SX3.1.1.944, XP SP2, 4GB RAM (1GB not accessible, but used just to balance the computer so it doesn't tip over); Delta 66 in Omni i/O Studio; Motif8; UAD-1
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Hugh Robjohns
SOS Technical Editor
Joined: 25/07/03
Posts: 18390
Loc: Worcestershire
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Re: normal EQ vs linear phase EQ
[Re: mjfe2]
#1038218 - 14/03/13 05:40 PM
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Quote mjfe2:
Hmm, just wanted to
re-open this discussion because I'm still not sure I understand how EQs put the signal out
of phase. If you EQ a single channel can its phase be affected?
We are all used to viewing the audio world
in terms of the frequency-amplitude response. That's how we draw filter shapes, and
measure the 'quality' of mics, speakers and equipment. But there is also a parallel
frequency-phase response -- the two go hand in hand. Changes to one always affect the
other in the analogue world.
Analogue world filters are built from resistors,
capacitors and inductors. The last two are fundamentally resonant energy-storage devices,
and consequently signals are delayed slightly as they pass through them -- the amount of
delay being dependent on the frequency.
As a result, every filter stage not
only affects the amplitude with frequency, but also the delay with frequency. In some
design circles engineers will talk of 'group delay', but in the audio world the delays are
generally tiny and manifest as relative phase shifts. So every device that has filters --
and they all do, even if only to set the bandwidth limits -- will also have a phase
response which varies with frequency.
Here's the phase response of a single
channel on the JDK 8MX2 mic preamp/mixer:
Although our ears are not very sensitive to
these typically small relative phase shifts at different frequencies, they do go some way
to affecting our perception of different 'flavours' of EQ. More importantly, we have all
become completely accustomed to the way analogue EQ alters relative phase with frequency
and that's what we expect to hear. These small phase shifts also affect the shape of the
amplitude waveform, because the different harmonics are moved in time relative to one
another through the action of EQ, as well as changing their amplitudes.
Most
digital EQs emulate analogue EQs and so also incorporate similar phase shifts as part of
the EQ itself. Linear-phase EQ deliberately doesn't do that... which can be useful in some
situations, primarily where you don't want to change the waveform envelope shape.
hugh
--------------------
Technical Editor, Sound On Sound
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mjfe2
Joined: 11/10/09
Posts: 504
Loc: Cambridge, UK
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Re: normal EQ vs linear phase EQ
[Re: Hugh Robjohns]
#1038233 - 14/03/13 06:36 PM
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Thanks, as always, Hugh! So is the frequency/phase response the reason why those recent
discussions about third-party EQs being no better than bundled DAW EQs are too simplistic?
I have to say, it's quite hard to think outside the frequency/amplitude box (especially
as it maps so neatly onto how we understand the two dimensions of musical notation!).
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mjfe2
Joined: 11/10/09
Posts: 504
Loc: Cambridge, UK
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Re: normal EQ vs linear phase EQ
[Re: Hugh Robjohns]
#1038891 - 19/03/13 03:57 PM
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Quote Hugh Robjohns:
We are all
used to viewing the audio world in terms of the frequency-amplitude response. That's how
we draw filter shapes, and measure the 'quality' of mics, speakers and equipment. But
there is also a parallel frequency-phase response -- the two go hand in hand. Changes to
one always affect the other in the analogue world.
On another note, how many manufacturers publish stats about the
phase response of their equipment? Would this be a useful measurement of quality? I'm
always baffled by how many preamps or interfaces, including budget offerings, quote flat
frequency responses of 20hz-20khz within a fraction of a decibel. Presumably this is
meaingless unless all the frequencies are in phase with each other as well?
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