Understanding the State of the Art of Digital Room Correction

[JRS]

acording to Mr Sbragion http://drc-fir.sourceforge.net/doc/drc.html#sec35

As a bystander, I would suggest some caution when it comes to drawing conclusions about timbral accuracy based on what cues improve speech intelligibility. There is likely some overlap, but we listen to music, not speeches.

 

[thorvat]

And, when averaged, assist in reducing measurement noise.
Which can lead to incorrect compensation if there are contributions to the signal that should be compensated for, but whose effects have been diminished by said averaging...

So, we have come to a point where wise words from @Sean Olive saying that avoiding a spatial averaging is not a good idea (btw, same thing said by @Floyd Toole in several papers he wrote) are now getting clouded with a foggy term "measurement noise, which can lead to incorrect compensation". Way to go guys, way to go..

 

[markus]

So, we have come to a point where wise words from @Sean Olive saying that avoiding a spatial averaging is not a good idea (btw, same thing said by @Floyd Toole in several papers he wrote) are now getting clouded with a foggy term "measurement noise, which can lead to incorrect compensation". Way to go guys, way to go..

I don't see things as black and white. I do believe that the right kind of measurements can give us information which could benefit "room correction". But, I also think not nearly enough is known psychoacoustically to make proper use of it.

 

[Frgirard]

So, we have come to a point where wise words from @Sean Olive saying that avoiding a spatial averaging is not a good idea (btw, same thing said by @Floyd Toole in several papers he wrote) are now getting clouded with a foggy term "measurement noise, which can lead to incorrect compensation". Way to go guys, way to go..

Olive and Toole will be the demiurges?

For the moment no mathematics can predict the type of correction to apply. Only empiricism like 17th century alchemy

The impulse response canot be averaging.

 

[mitchco]

Again, what do you want to see? I'm not the one making claims here unless you think that stating "there's not enough scientific studies" is a claim that can be proven with measurements...

You can start with this one:

Multiple measurements help in identifying the modal behavior of a room and how it can effectively be corrected using PEQ. A single point measurement isn't enough.

Remember, your own measurement data to show that a single point measurement is not enough, say using Acourate since you already have that.

 

[markus]

Olive and Toole will be the demiurges?

For the moment no mathematics can predict the type of correction to apply. Only empiricism like 17th century alchemy

The impulse response canot be averaging.

You can "scan" a room using multiple measurements and determine where to best put subs. It can also tell you what PEQ settings would cut down the peaks. Let's also bring on Todd Welti

 

[tecnogadget]

You can "scan" a room using multiple measurements and determine where to best put subs. It can also tell you what PEQ settings would cut down the peaks. Let's also bring on Todd Welti

Now you are changing things. Of course you should take measurements with REW to determine the best spot for speaker/sub placement, but thats before taking the actual measurement that Mitchco proposed for DSP.

 

[markus]

Now you are changing things. Of course you should take measurements with REW to determine the best spot for speaker/sub placement, but thats before taking the actual measurement that Mitchco proposed for DSP.

Not trying to change the topic. I was specifically responding to Frgirard. I've mentioned taking multiple measurements for best placement of subs just because ANY room correction approach is omitting this step. Much better results could be had. Actually Welti's SFM can do such an optimization. You could probably also use MSO.

 

[mitchco]

Multiple measurements can actually reduce the resolution of the correction at the listening position. This was mentioned in Sean Olives study on, “The Objective and Subjective Evaluation of Room Correction Products. See: https://www.audiosciencereview.com/...review-room-eq-setup.26397/page-9#post-906241 You can hear it in AB tests, which I have done, and encourage others to compare and hear with your own ears.

I have also measured the reduction in resolution:

I took sweeps of two correction filters through the convolution engine so we can see each filter that is being applied to the same loudspeaker system in the same room. The top correction filter is Dirac's using their recommended multiple measurement approach and the bottom is one of the DRC packages discussed using a single measurement. The red line can be considered 0 dBFS for the bottom correction as it is cut only with no boosting.

As one can see, below 600 Hz, the Dirac correction has significantly less frequency correction resolution than the other correction filter. And the Dirac filter is over correcting at 95 Hz. As one should be able to glean, the audible differences between the two filters is significant in AB testing.

On a slightly different note, Dirac uses a mix of IIR and FIR filters. IIR filters are used at the low frequencies and therefore offers no excess phase correction at low frequencies to correct for the rooms non-minimum phase response.

Don't get me wrong, I have reviewed Dirac extensively here. But because of these audible/measurable shortcomings, it did not make the SOTA list. Which is what this post and video is all about.

If you disagree, fine. But show some data/measurements/listening tests to support your position. So far I see a lot of words, but no real data.

 

[Newman]

Again, rather that posting marketing material, how about you post some of your own data and measurements that you have taken to support any of your claims.

You ask for measurements, so he supplies measurements and commentary, but because they come from a company, you dismiss them outright with a put-down and…ask for measurements???

Not impressed.

 

[Newman]

Olive and Toole will be the demiurges?

You have the award for Word of The Day!

 

[dasdoing]

As a bystander, I would suggest some caution when it comes to drawing conclusions about timbral accuracy based on what cues improve speech intelligibility. There is likely some overlap, but we listen to music, not speeches.

the concept has actualy been included in the field of timbral accurancy: https://www.researchgate.net/public...ption_of_Family_and_Register_in_Musical_Tones

 

[j_j]

Latency with ultra long FIR filters: The signal has to pass the whole filter first before sound comes out at the end. This prohibits such filters for any application that requires (near) realtime processing like gaming or really any video streaming. One could build a video buffer to sync audio and video but at this point such a solution does NOT exist in consumer AV space (and the gaming problem remains).

Uhhh. NO.

It is possible, indeed probable, that one might build an FIR in a minimum-phase configuration. For such, preloading with zeros can eliminate all but processing latency.

Symmetric FIR's are absolutely, positively NOT what you want for room correction. Nope.

 

[j_j]

"strong arguments and experimental evidence" is not the same as "scientific study"
And, what smoothing is "correct" in order to create the "right" spectral envelope?

Really? So you deny the bandwidths of the hearing apparatus (i.e. ERB, cochlear filters, etc) that define where and what is audible?

You're dismissing all psychoacoustic research out of hand?

 

[j_j]

Denis uses ERB,

but imo no smoothing should be used at all. and FDW doesn't make sense either with this concept, unless you hear an echo

Well, then, you'd be wrong, for both acoustic and psychoacoustic reasons.

Corrections with a tiny width are incredibly position dependent. You'll never get it right for both ears at the same time. Remember, correction bandwidth times wavelength tells you a rough estimate of how far before you go completely wrong (note, there is another factor there under 1/2 but that depends on the tolerance you prefer).

Furthermore, that means longer filters, and much more chance of engaging nonlinearities in the auditory system, which can make "better via LMS" sound worse in practice.

All of this is testable and verifiable. Those who reject the actual behavior of the ear are simply scoffing at the science.

 

[j_j]

As a bystander, I would suggest some caution when it comes to drawing conclusions about timbral accuracy based on what cues improve speech intelligibility. There is likely some overlap, but we listen to music, not speeches.

Speech intelligibility is a completely different critter. EOF.

 

[j_j]

I don't see things as black and white. I do believe that the right kind of measurements can give us information which could benefit "room correction". But, I also think not nearly enough is known psychoacoustically to make proper use of it.

Oh, come on. Basic study of ERB's, cochlear filter responses, etc, makes a lot of things entirely clear. That includes need for smoothing, attention to correction filter phase issues, consideration of the wavelengths being considered, as well as gross things like first arrival timbre and timing.

 

[j_j]

You can start with this one:



Remember, your own measurement data to show that a single point measurement is not enough, say using Acourate since you already have that.

Uh, for this, using ambisonics (not my favorite tool, but for this it's good) or related techniques actually helps with that.

AES Convention Papers Forum » DTS Multichannel Audio Playback System: Characterization and Correction

The AES Forum is where our members get to interact with each other in between conferences and section meetings.

secure.aes.org

In particular, by capturing the volume velocities in a room, we can very nicely recognize the stored energy in a room.

 

[fluid]

Symmetric FIR's are absolutely, positively NOT what you want for room correction. Nope.

What do you think is the right type of filter and why is a symmetric FIR wrong?

 

[j_j]

uh, asked and answered? You did see the comment about "minimum phase"? right? Hello? I guess I will add the potential for surprising pre-echo if there's any overcorrection at all.

Adding, that slide 52 of this shows 3 examples of FIR filters with precisely (to numerical limits) the same frequency response.
Minimum phase, constant delay (aka linear phase), and maximum phase. I don't presently have a good discussion on line with recorded talk on how to do it, but it's in the literature.

http://www.aes-media.org/sections/pnw/ppt/jj/src1_9_16.pptx

Further adding that if you have a minimum phase system, another minimum phase system can correct it. Now, acoustic systems do not have to be anything at all like minimum phase, but there is a large part that is, and you're not going to correct the rest (for phase) without getting into linearity issues in hearing.