My Lyngdorf DPA-1 sure does the trick without changing the music (I've done exaustive listening testing around this using my prior preamp Ayre K-1xe). I'm not sure if you can only correct a certain frequency, but maybe you don't need to?
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Why does it need to be digital? If you want the purest way to deal with room modes operating 350 Hz and below and not messing with the signal above why not use the Rives Audio PARC. Here's a link to a reveiw.
It's certainly better if you go from digital out to processor before converting to analog. Not everyone has a separate transport (or source) and DAC, in which case an additional D/A and A/D is required. Even so, I do not agree that the digital correction is better. There are some that are good, and others are horrible due to digital artifacts. Some use very steap slopes and sampling of curves that cause a ringing artifact. My graduate work was in digital signal processing and I know the caveats of attempting this in the digital domain. This is the main reason we went to an analog only domain system.
I'm still curious from Sashav's point of view why digital for his application.
it robbed music of transients, dynamics and details were seriously affected.
I think you have to get used to it. If you have been living with room modes for a while then the presentation seems kind of exaggerated and you can get used to the larger than life presentation (like having lived with the contrast always jacked up all the way on a TV - either a note is very strong or it disappears in a deep null - very lively but unrealistic and lacking nuance)
I would not try to do much above 100 Hz in terms of adjustments and of course only on peaks. 100 Hz is 10 feet so a quarter wavelength is 2.5 feet and you are getting down to the sweetspot size.
Bear in mind you have to do room treatments first - as the nulls cannot be corrected for except by improving acoustics - so for sure it sounds dull if you have no bass traps even if you have EQ'd to remove modal peaks.
I agree about ringing of filtering can in general be a problem and fast digital filters with short taps are not always of highest quality and extreme settings can lead to ringing and phase problems.
FWIW I'd recommend only EQ the sub and don't aim for anything near perfect flat - just get the worst 10 or 15 db broad bumps reduced to a reasonable size (no more than +6 db and your ears/brain will handle the rest) and preferably don't try to EQ the main speakers - just in case you muck up the mid bass and lower midrange from digital filter ringing or phase issues. Remember that above 140 Hz you begin to hear directionally so I would not recommend mucking about with sharp (high Q) filters that may affect phase.
One advantage of digital filtering is the phase behaviour can be better controlled.
Shadorne, I do not have the sub.
My speakers are PMC IB2, two channel.
Humps are 50Hz on left channel and 40Hz and 70Hz on right channel, quite severe, somewhere around 8dB.
BTW, I drove to States to hear active ATC50s, setup was not that great (they did not get them stable enough on the spikes, they were somewhat wobbly), quite similar to PMC as far as midrange goes (which I could never give up), but overall I have not heard any reason to switch, so I am sticking to PMCs, seems I will be buried with them.
PMC used ATC midrange in the past. PMC are absolutely excellent speakers. I think they use Volts on the woofers but the design is similar to ATC but with more bass (TL design). If you already own PMC then I am not surprised you heard no reason to change. ATC probably have the edge with classical listeners and PMC probably has the edge with rock (more bass) but it is indeed a close call and at the end of the day a matter of taste. I'd probably be just as happy with PMC.
Humps are 50Hz on left channel and 40Hz and 70Hz on right channel, quite severe, somewhere around 8dB
That is actually not bad at all, IMHO. If you tried to hammer that all flat then I am not surprised that it might not pass for an improvement. Of course, the nulls are the worst....as certain bass notes just disappear.
Your post makes it sound like Sashav and others would need new equipment which is totally false. Almost every high end CD player allows the D/A conversion to be bypassed so no one has to buy new equipment to use the Lyngdorf room correction equipment. This is no more complicated than using a digital out from your CD player which is usually toslink or digital RCA and occassionally XLR.
Sashav, a digital box like the DEQX can do a number of things that can not be done in the analogue domain. Well, some of these things CAN be done, but not without a lot of experimentation and a lot of extra circuitry in the box. If you compare a product like the DEQX with a Marchand XM144 crossover, these are the advantages of the DEQX:
- steep crossover slopes, up to 100dB/oct. Marchand can only do 24dB/oct and introduces phase issues. The Marchand's x-over point and slope can be adjusted by purchasing a card ($10) compared to a few clicks of a mouse button with the DEQX.
- group delay. Both products implement this, DEQX via your laptop and Marchand via a drop in card.
- room correction. DEQX can correct a near infinite number of frequencies. Marchand attenuates or boosts selected frequencies via insertion of notch filters.
On the face of it the DEQX is more flexible and easier to tune. However (as I have said many times) the problem with the DEQX is that it drags the overall quality of your system down. I have heard a DEQX with a high quality analogue source. It makes the turntable sound like a cheap CD player.
The biggest problem is (as you say) it robs the sound of dynamics and subtlety. The frequencies that suffer the most are the midrange and treble. If you could think of a way to use the DEQX only in the most problematic frequencies - 200Hz and below - you would have the best of both worlds.
I recently experienced an audio epiphany with the DEQX. I now recognize that room correction alone provides some benefit, but is nothing compared to correction of phase and group delay.
The other gotcha - DEQX is very system dependent. On my system it brought obvious benefits along with obvious losses. I would have to give up some things (transparency, dynamics, resolution) to gain others (coherency, accuracy). How much YOU benefit would depend on the balance of faults and strengths of your system. So I would shy away from making an endorsement of this product, or any other product.
Mmike: It's true most CD players have digital out--but in that case where will you do the D/A. Most Cd players do not have a digital input. Some very high end ones do, but most don't. And I'm also considering the possibility of analog sources such as a turntable or tuner. I did not mean to imply "you have to buy new equipment." I was only trying to point out some potential caveats. That's to say there is one and only one way to accomplish the goal. It's more a matter of helping those reading this post to define their goal and then what approach might work best. Obviously, it's not the same answer for everyone.
I was assuming Sashav has a preamp with phono or if not, and he needs it, he could add a separate phono stage. Your last post says most CD players don't have a digital in but I think you meant out which I don't agree with. Most high end one box CD players do have a digital out, and a high end transport would work even better. While it's true the D/A conversion has to happen somewhere but in the case of the Lyngdorf room perfect system the unit has an excellent D/A in it.
Thanks for clarifying though (and responding to my post!) as I felt your first post suggested Sashav would need new equipment and should abandon digital correction which may not the case. In the end I strongly suggest keeping an analog or digital source as far as possible. Thanks for clarifying. I think we're both making useful suggestions so Sashav can make the best improvements he can. :)
Mike--I actually did mean digital end. My point was getting a really good D/A conversion. You are right most CD players do have digital out--but my concern was where will the D/A conversion take place. If the CD player is a top shelf unit you wouldn't want to just use the digital out and convert D/A with something that's not up to par. What would be pretty nice is if you could go digital out to a really good digital processor and then back to a top shelf D/A. This would work great if you used separate transport and DAC or in the rare event the CD player did have a digital in. However, this obviously limits the sources that would be corrected.