Planar Speaker Asylum

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RE: digital roomcorrection

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In Reply to: RE: digital roomcorrection posted by joaidferg on January 19, 2011 at 04:58:59

DEQX, as I understand it, takes two sets of measurements, a gated nearfield one to derive compensation curves for frequency and phase anomalies in the loudspeaker itself, and one at the listener's position to compensate for room anomalies.

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RE: digital roomcorrection - hemholtz 11:10:17 01/19/11 (15)
that's exactly how it works. the parametric eq is for "room correction" and the filters are for "speaker correction". once the speakers are corrected, you still have to get the mid and high frequencies to your ears without messing the whole thing up. if you have early reflections there is no "room correction" that can fix that. you might be able to smooth the frequency response a little but it will still be comb filtered and not as realistic.
- RE: digital roomcorrection - josh358 08:37:06 01/20/11 (14)
  Yeah, I don't see any way you can compensate for comb filtering above a certain frequency, since it will change as you move your head relative to the room surfaces. So the best course seems to be to limit most room compensation to low frequencies. Even then, the corrections will only be good at one point in the room or will represent a compromise over a larger area.
  - RE: digital roomcorrection - hemholtz 06:46:49 01/21/11 (11)
    that is why i like very narrow cuts for room correction. test tones help you find the exact frequency of the problem modes, but music is not test tones. even a bass note played by a musical instrument with the exact same fundamental frequency will sound much closer to "normal" with only that narrow cut.
    - RE: digital roomcorrection - josh358 07:39:24 01/21/11 (10)
      I don't know about you, but I've always found that moderately broad equalization can do more violence to the sound than no equalization at all. Newer research says that we're much more sensitive to low Q than high Q resonances -- the opposite of what I would have thought -- and I suspect that that's the reason. It seems that equalization has to have a 1/12 octave resolution to be effective.
      - RE: digital roomcorrection - hemholtz 09:05:52 01/21/11 (9)
        
        In Reply to: RE: digital roomcorrection posted by josh358 on January 21, 2011 at 07:39:24
        
        1/12 octave is the narrowest choice in the deqx parametric eq. that's exactly what i meant by narrow.
        
        RE: digital roomcorrection - josh358 11:45:32 01/21/11 (8)
        
        In Reply to: RE: digital roomcorrection posted by hemholtz on January 21, 2011 at 09:05:52
        
        Do they also give you manual control over group delay?
        
        RE: digital roomcorrection - hemholtz 12:06:30 01/21/11 (7)
        
        In Reply to: RE: digital roomcorrection posted by josh358 on January 21, 2011 at 11:45:32
        
        if you mean by channel, then yes. you can apply a delay to each channel on the crossover independently. you can't pick a group of frequencies to delay though. i'm not sure why you would want to do that since it does a good job automatically from the speaker measurements.
        
        RE: digital roomcorrection - josh358 15:50:28 01/21/11 (6)
        
        In Reply to: RE: digital roomcorrection posted by hemholtz on January 21, 2011 at 12:06:30
        
        Well, comb filtering isn't minimum phase, so I was thinking that the room corrections could leave you with group delay.
        
        RE: digital roomcorrection - hemholtz 17:32:08 01/21/11 (5)
        
        In Reply to: RE: digital roomcorrection posted by josh358 on January 21, 2011 at 15:50:28
        
        the comb filtering i'm talking about is at higher frequencies not effected by room dimensions but by early reflections. room correction are at lower frequencies. the time between + and - is greater at these frequencies. there are much bigger problems reproducing these frequencies than group delay.
        
        RE: digital roomcorrection - josh358 18:01:16 01/21/11 (4)
        
        In Reply to: RE: digital roomcorrection posted by hemholtz on January 21, 2011 at 17:32:08
        
        That's true. At those frequencies, you're lucky if you can just get something that's reasonably flat.
        
        RE: digital roomcorrection - hemholtz 06:27:37 01/22/11 (3)
        
        In Reply to: RE: digital roomcorrection posted by josh358 on January 21, 2011 at 18:01:16
        
        decay of modal frequencies is what muddies it all up. a little bump in frequency response isn't all that bad, but slow decay of that bump sounds terrible. it covers up important harmonics and makes the bass line sound monotone. the best thing to do is a 1/12 octave 6db or better cut centered on the modal frequency. you will still hear the modal frequency but the decay will be 10db down right away and will usually drop off much quicker after that too.
        
        RE: digital room correction - josh358 05:53:00 01/23/11 (2)
        
        In Reply to: RE: digital roomcorrection posted by hemholtz on January 22, 2011 at 06:27:37
        
        Not to mention that you get pitch shift, a truly bizarre phenomenon. But I'm curious -- are you talking about adjusting the equalizer so that the time-integrated 1/12 octave frequency response is flat, or are you talking about pushing the band down even further because the time smear of the resonance is sonically worse than the resulting frequency response dip?
        
        RE: digital room correction - hemholtz 08:47:39 01/23/11 (1)
        
        In Reply to: RE: digital room correction posted by josh358 on January 23, 2011 at 05:53:00
        
        sometimes a 10 db cut only makes a 3db difference on stacked modes. i wouldn't call it a smear, just slow in room decay.
        
        it's mostly just trial and error. measure, adjust, remeasure, listen to results. i just put the deqx eq window next to the etf5 low frequency measurement window and click away. once the measurement mic is set up and the software configured, it usually doesn't take more than an hour for really good results.
        
        RE: digital room correction - josh358 10:34:01 01/23/11 (0)
        
        In Reply to: RE: digital room correction posted by hemholtz on January 23, 2011 at 08:47:39
        
        You're giving me a bad case of DEQX envy. Though I'd still like to do this in software if possible, since I can't afford to use DEQX for surround.
  - RE: digital roomcorrection - hemholtz 11:12:28 01/20/11 (1)
    the only way to fix the comb filtering is to fix the early reflections. from my experience, anything substantial within 15ms on an impulse response measurement is going to effect music adversely.
    - RE: digital roomcorrection - josh358 11:21:37 01/20/11 (0)
      I think that may be the most intractable problem in high-end consumer audio: how do you suppress those early reflections in moderately-sized rooms without acoustical treatments that have the wife acceptance factor of a rotten squid?

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