DRC, Digital Room Correction- is it the poor relation to Room treatments?

Audiophile Neuroscience · February 27, 2015

Hi Barry,

again many thanks for sharing your experience and knowledge.

I understand that DSP may alter the attack time to better align or make drivers more coherent. This would help poorly designed speakers but still skew the direct response of the speaker - so a win/lose scenario. What about DSP in ameliorating first reflections, can that be helpful (albeit once again at the cost of skewing the direct response) ?

You have some great info on your site about setting up a listening/monitoring space (I cant access your site atm so cant link to it). Do you have any other recommended sites dealing with room treatments and speaker positioning ?

Cheers

David

bdiament · February 27, 2015

Hi Barry,
again many thanks for sharing your experience and knowledge.

I understand that DSP may alter the attack time to better align or make drivers more coherent. This would help poorly designed speakers but still skew the direct response of the speaker - so a win/lose scenario. What about DSP in ameliorating first reflections, can that be helpful (albeit once again at the cost of skewing the direct response) ?

You have some great info on your site about setting up a listening/monitoring space (I cant access your site atm so cant link to it). Do you have any other recommended sites dealing with room treatments and speaker positioning ?

Cheers

David

Hi David,

Properly designed and implemented DSP should be able to manipulate attack time without necessarily skewing the direct response of the speaker. In some instances DSP *should* be used to skew an already-skewed direct response from a poorly designed speaker. Note that attack time manipulation and frequency response manipulation are not the same thing. However, if the speaker is really that poorly designed, I would not expect DSP to make it sound like it was well designed.

The above is about using DSP to manipulate loudspeaker response, not room response. I always say I find it preferable to address problems at their source. Altering the response of the speaker *may* be helpful when the problems are in the speaker. It is altering the response of the speaker in the attempt to address problems in the *room* that, in my opinion, doesn't work because the speaker gets skewed and the room issues remain.

In my view, DSP can successfully be used to tame early reflections *only* if it is used to completely eliminate loudspeaker response at *all* frequencies. Turning the speakers off will accomplish the same thing. ;-}

Think of room surfaces as mirrors. If you don't want to "see" a reflection, what can you do? Will changing the response of the loudspeakers in either amplitude or time prevent you from seeing their reflections? The only way I know to block a reflection is to cover the "mirror" in those areas from which the reflection originates. It is the same with sonic reflections: the application of a soft, absorbent (i.e., non-reflective) material at the reflection point will do the job.

Note that only as much of the surface as provides the reflection must be covered. In some instances, folks mistakenly think that if a little is good, more must be better. Too much absorption will result in an uncomfortable, dead-sounding space. Only those early reflections need to be absorbed. Go back to imagining the room as all mirrors and from the listening position you'll "see" one reflection of each speaker on each room boundary.

In addition to my article on setting up a room, there is an entry in the Soundkeeper blog. I've also found a few good articles on the ASC site, including this one (but in this particular article, one must extract what is useful from the rest).

As to speaker positioning, like everything else in audio, it seems that if you ask three folks, you'll get at least four different answers (five of which may well be wrong ;-}). Personally, I think Peter Walker nailed it in the mid-1950's in what he wrote for Wireless World. Don't have a link to that though.

Best regards,

Barry

Measuring Loudspeakers, Part Two Page 3 | Stereophile.com

Audiophile Neuroscience · February 28, 2015

Barry,

Thanks for the additional clarifications, links and references. Much appreciated.

Cheers

David

dallasjustice · February 28, 2015

David,

Your last question on direct of examination to your witness needs more information. There are different types of "reflections" in a room. Some of those reflections are good and can add to spatial detail and even coherence as Toole/Olive proved at Harman. However, there are other types of reflection which are bad. In this category there are two types to consider for the purposes of DSP: minimum phase and non-minimum phase. As pointed out by many including Toole, there is a direct mathematical relationship between the speaker response and the minimum phase decay time in the room. The decay time may or may not matter depending on the Q of the modal peak and the corresponding decay time. In short, minimum phase SPL phenomenon CAN be inverted to obtain better frequency response and phase response. None of this is subject to debate. It's a fact. These minimum phase modal peaks which can be inverted are almost always at very low frequencies; say below 200hz. At these frequencies there is no "attack" from the speaker. It is a myth to think of low frequency as having attack or a leading edge. Just look at the impulse response for a 50hz cycle. It's REALLY wide and difficult to eye ball the peak. John Atkinson wrote a little here about woofers in the time domain.

IOW, if you have a medium Q , 15db axial mode at 50hz, you will hear the room and NOT the speaker at that frequency.

There are other non-minimum phase reflections. These are most likely going to be an SBIR. Forumers call this a "null". These phenomena SHOULD NOT be corrected with DSP if the reflected sound is equal to or greater than the original wave. This can be easily seen in REW with the excess group delay function.

Read John Mulcahy. He explains it better than anyone.

Minimum Phase

So what I'm saying is that your obtuse direct examination question to Barry about reflected sound assumes that the engineers who design softwares like REW, DIRAC live, Audiolense, Acourate or Harman's ARCOS are all ingorant about basic room physics and that a simple minded explanation about speaker precedence effect covers the whole topic of DSP.

Michael.

Audiophile Neuroscience · February 28, 2015

Michael,

I asked about first reflections, for me meaning the first reflected sound waves reaching the listening position having bounced off walls,floor and ceiling.This arrives, as you know, some time after the first wave of direct sound from the speakers. I asked Barry whether DSP could ameliorate the deleterious effects of such waves.

I am honestly at a complete loss as to how you considered that an "obtuse direct examination question to Barry about reflected sound assumes that the engineers who design softwares like REW, DIRAC live, Audiolense, Acourate or Harman's ARCOS are all ingorant about basic room physics and that a simple minded explanation about speaker precedence effect covers the whole topic of DSP."

Thank you for the extra info though, appreciated

Cheers

David

dallasjustice · February 28, 2015

If you took time to read the stuff I linked to, you would understand why your question is totally inapplicable to the DSP softwares mentioned in this thread. There are different types of reflections. Calling it a first reflection still doesn't having anything to do with DSP. IF the first reflection has an SBIR causing a deep null, most DSP won't touch! Otherwise, DSP doesn't claim to alter the speaker off axis. So, why would you even ask such a question?

Michael,
I asked about first reflections, for me meaning the first reflected sound waves reaching the listening position having bounced off walls,floor and ceiling.This arrives, as you know, some time after the first wave of direct sound from the speakers. I asked Barry whether DSP could ameliorate the deleterious effects of such waves.

I am honestly at a complete loss as to how you considered that an "obtuse direct examination question to Barry about reflected sound assumes that the engineers who design softwares like REW, DIRAC live, Audiolense, Acourate or Harman's ARCOS are all ingorant about basic room physics and that a simple minded explanation about speaker precedence effect covers the whole topic of DSP."

Thank you for the extra info though, appreciated

Cheers

David

jiminlogansquare · February 28, 2015

I'm just going to state here that iRC (what Amarra calls its version of Dirac) has had a significant positive effect on the sound of my system. Some of that is in the realm of frequency/EQ, yes; but some is in the realm of impulse response. I think this might be why Amarra has emphasized impulse response control in the name of its product (that is what "iRC" stands for).

Take a look at the following screenshots. White lines are "Before iRC" and green are "After iRC." Clearly something measurable is going on. I will add to this that the PRAT, bass, and to some degree soundstage and imaging have all improved from adding iRC to the mix

Earlier versions of these graphs showed more extreme corrections by iRC. As a result of seeing just how much heavy lifting iRC was doing in those earlier tests, I've done things like move my speakers and listening chair closer together to reduce room acoustic effects; the shots below are of my current furniture/speaker layout (one that I probably cannot alter much more ... this is after all a living room I share with my wife, not a dedicated sound examination bunker).

Audiophile Neuroscience · March 1, 2015

IF the first reflection has an SBIR causing a deep null, most DSP won't touch! Otherwise, DSP doesn't claim to alter the speaker off axis. So, why would you even ask such a question?

Michael,

I asked the question as I was genuinely curious. AFAIK the topic hadnt been raised before and I wondered about it. Whether DSP/DRC progams do or do not *claim* to alter off axis response, early reflections or anything else is not the point, I still wondered about it.The issue of filters and phase was, to my understanding, already addressed by Barry. I asked the question of Barry because, well,to state the obvious, I wanted Barry's opinion. I assumed if he thought the filters or phase was relevant he would have mentioned it. Barry kindly answered my question. Made sense to me. Not sure why that challenges your whole ideology.

Cheers

David

dallasjustice · March 1, 2015

There is nothing challenging to your questions or Barry's answers. I am trying to clarify erroneous thinking and assumptions being made. However, if Barry's logic makes you feel better, then you have all the answers you need.

Michael,
I asked the question as I was genuinely curious. AFAIK the topic hadnt been raised before and I wondered about it. Whether DSP/DRC progams do or do not *claim* to alter off axis response, early reflections or anything else is not the point, I still wondered about it.The issue of filters and phase was, to my understanding, already addressed by Barry. I asked the question of Barry because, well,to state the obvious, I wanted Barry's opinion. I assumed if he thought the filters or phase was relevant he would have mentioned it. Barry kindly answered my question. Made sense to me. Not sure why that challenges your whole ideology.

Cheers

David

jiminlogansquare · March 1, 2015

Just as another reference point, I dug up a little active subwoofer that was gathering dust in my closet for the past 10 years or so (certainly not an audiophile product; it's a Miller & Kreisler Model K98K). Plugged it in, set the Low Pass Filter at 50 Hz (based on the fact that my PSB Synchrony 2's seem only to have problems below 40 Hz), set the gain to "Moderate," and re-ran my iRC (Dirac) project and created a new filter. Well, it sounds pretty OK, for such a Frankenstein's monster. And for reference sake, here are screen prints from iRC (Dirac) showing what I'm now dealing with (and I can assure you that the bass, including in "spectaculars" like the Keith Johnson Minnesota Orchestra/Reference Recording Stravinsky Firebird) are well presented):

Audiophile Neuroscience · March 1, 2015

I am trying to clarify erroneous thinking and assumptions being made.

Suggest you ask Barry

However, if Barry's logic makes you feel better, then you have all the answers you need.

Well put another way, I am very happy with both Barry's logic and answers

Cheers

David

Audiophile Neuroscience · March 1, 2015

@ Barry (or others)

One area of controversy (for me) re room acoustics remains "matching the speaker to the room", both physically and acoustically. There are some obvious issues with physical dimensions of the speaker but there are also things like bass driver diameter vs room volume, height of speaker vs ceiling height etc. Then there is the issue of full range speakers generating low bass. You have been most generous with your time so just some recommended articles, if any come to mind, would be great.Thanks

David

bdiament · March 1, 2015

Suggest you ask Barry

Well put another way, I am very happy with both Barry's logic and answers

Cheers

David

Thank you again David.

I mentioned earlier that my experience has been that folks don't argue about that in which they are confident. I'm a bit surprised at how the civility quotient seems to be going down simply because I don't share the perspective that skewing a speaker's response improves the sound of a room (and does not also harm the sound of the speaker). I know some folks feel differently and celebrate their happiness with their systems. I wonder why they have trouble doing the same.

And why in the world do some folks insist on arguing about audio?!?!?

This only brings Pirsig to mind and his statement that no one argues that the sun is going to rise tomorrow - they know it will. Folks only argue about that in which they are not confident. I believe Pirsig nailed this one.

Neither do I share the perspective that low frequencies don't have an attack or a leading edge. (This may well be true however when listening to a bad or poorly set up system.) I would have thought that anyone who has ever heard a bass drum or a thunderclap would realize this isn't true. At least based my own limited experience in life, I'd say there are some pretty steep low frequency wave fronts in the real world.

As to the assertion that the direct sound from the speakers, having a physically shorter distance to travel, arrives at the listener's ears ahead of sounds from the room, is "simple minded" well, I suppose that is one way to look at it. It is a simple reality, even if the pejorative implication of that statement is sad. I don't know, maybe I'm completely off base but it sure seems to me (both theoretically and experientially) that given a constant speed, the shorter distance will be traversed sooner. Some folks will not hear the time differential. Some will.

Best regards,

Barry

http://www.soundkeeperrecordings.com

http://www.barrydiamentaudio.com

bdiament · March 1, 2015

@ Barry (or others)
One area of controversy (for me) re room acoustics remains "matching the speaker to the room", both physically and acoustically. There are some obvious issues with physical dimensions of the speaker but there are also things like bass driver diameter vs room volume, height of speaker vs ceiling height etc. Then there is the issue of full range speakers generating low bass. You have been most generous with your time so just some recommended articles, if any come to mind, would be great.Thanks

David

Hi David,

I'm afraid I don't know of any articles on this subject that I can recommend. Perhaps because I don't necessarily subscribe to the idea that the speaker must be matched to the room. I've heard some big speakers sound absolutely wonderful in small rooms.

Here too, I see the speaker and the room as two different things. The speaker will excite the room and the room will respond to how the speaker excites it, but they remain two things, each of which I address separately.

I really can't say that in a room of such and such dimensions, I'd use woofers of such and such driver area. (I say area as opposed to diameter because not all drivers are round.) Same with height. Is there something specific you have in mind?

Best regards,

Barry

dallasjustice · March 1, 2015

Neither do I share the perspective that low frequencies don't have an attack or a leading edge. (This may well be true however when listening to a bad or poorly set up system.) I would have thought that anyone who has ever heard a bass drum or a thunderclap would realize this isn't true. At least based my own limited experience in life, I'd say there are some pretty steep low frequency wave fronts in the real world.

Best regards,

Barry

Soundkeeper Recordings

http://www.soundkeeperrecordings.wordpress.com

Barry Diament Audio

I've played drums in various rock cover bands for many yeas. I am familiar with a kick drum. The "attack" your perspective hears is actually the mallet slapping the drum head, which is not a low frequency:

bdiament · March 1, 2015

I've played drums in various rock cover bands for many yeas. I am familiar with a kick drum. The "attack" your perspective hears is actually the mallet slapping the drum head, which is not a low frequency...

Hi Michael,

Please forgive me but while you know what you hear, you don't know what I hear.

If you read what I wrote, you'd see that I said the bass drum, not the mallet. Here as elsewhere, two different things.

In my case, both my "perspective" and my ears hear bottom from a bass drum and that bottom has an attack and a wavefront. Same as the pluck of a low E string on a bass, same as a low E on a piano, same as any other sound, at any frequency, that must travel through any medium. I understand you may not experience it the same way.

Best regards,

Barry

Audiophile Neuroscience · March 2, 2015

Hi David,

I'm afraid I don't know of any articles on this subject that I can recommend. Perhaps because I don't necessarily subscribe to the idea that the speaker must be matched to the room. I've heard some big speakers sound absolutely wonderful in small rooms.

Here too, I see the speaker and the room as two different things. The speaker will excite the room and the room will respond to how the speaker excites it, but they remain two things, each of which I address separately.

I really can't say that in a room of such and such dimensions, I'd use woofers of such and such driver area. (I say area as opposed to diameter because not all drivers are round.) Same with height. Is there something specific you have in mind?

Best regards,

Barry

Soundkeeper Recordings

www.soundkeeperrecordings.wordpress.com

Barry Diament Audio

Hi Barry,

Thanks for your reply.

Well, I guess the most common things I have read is that large woofers moving lots of air will excite resonances in small rooms more than in larger volume rooms. This assumes the partcular resonance is there to be excited by those larger volumes of air.

With regards to full range speakers is there any rationale to avoid lower bass frequencies in small rooms.

With regards to height I have read that in rooms with low ceilings, tall speakers will lead to more comb filtering.

Generally my impression is that speakers do not have to match the room size. As you say each are different things but was curious as to your thoughts as to their interaction.

Cheers and thanks again

David

Audiophile Neuroscience · March 2, 2015

Hi Michael,

Please forgive me but while you know what you hear, you don't know what I hear.

If you read what I wrote, you'd see that I said the bass drum, not the mallet. Here as elsewhere, two different things.

In my case, both my "perspective" and my ears hear bottom from a bass drum and that bottom has an attack and a wavefront. Same as the pluck of a low E string on a bass, same as a low E on a piano, same as any other sound, at any frequency, that must travel through any medium. I understand you may not experience it the same way.

Best regards,

Barry

Soundkeeper Recordings

www.soundkeeperrecordings.wordpress.com

Barry Diament Audio

+1

bdiament · March 2, 2015

Hi Barry,
Thanks for your reply.

Well, I guess the most common things I have read is that large woofers moving lots of air will excite resonances in small rooms more than in larger volume rooms. This assumes the partcular resonance is there to be excited by those larger volumes of air.

With regards to full range speakers is there any rationale to avoid lower bass frequencies in small rooms.

With regards to height I have read that in rooms with low ceilings, tall speakers will lead to more comb filtering.

Generally my impression is that speakers do not have to match the room size. As you say each are different things but was curious as to your thoughts as to their interaction.

Cheers and thanks again

David

Hi David,

Every room will have its resonances, the frequencies of which will be dependent on the room's dimensions. There is a fundamental resonant frequency (i.e., mode) and its accompanying harmonics, for each room dimension. Only the resonant frequencies (and their first couple of harmonics) can be excited.

A given woofer in two different rooms, will excite the resonances (and harmonics) of each of the rooms. I do not see any reason to avoid having wide range speakers (those that deliver low bass) in any room. Treating the room will tame its resonances and harmonics and allow whatever the speaker is "saying" to be heard more clearly.

As to tall speakers in short rooms, it depends on the speaker and it depends on what, if anything is done to the room. Comb filtering can result, even from short speakers in tall rooms, if there is sufficient energy and reflections cause cancellations at the listening position. Here too, I find this is a matter of set up and room treatment and is unrelated to speaker or room height. Further, certain types of speakers, like planar dipoles and line sources do not radiate much energy vertically (with planners, not much to the sides either - so that type starts off with 2/3 of the room excitement potential gone).

I would put any speaker I wanted in any given room. From there, just as with any speaker in any room, it is a matter of proper placement of speakers, listening position, and everything else in the room - and proper room treatment, ideally trapping the bass in the pressure zones, absorbing early reflections and diffusing later ones.

Best regards,

Barry

Audiophile Neuroscience · March 2, 2015

Hi David,

Every room will have its resonances, the frequencies of which will be dependent on the room's dimensions. There is a fundamental resonant frequency (i.e., mode) and its accompanying harmonics, for each room dimension. Only the resonant frequencies (and their first couple of harmonics) can be excited.

A given woofer in two different rooms, will excite the resonances (and harmonics) of each of the rooms. I do not see any reason to avoid having wide range speakers (those that deliver low bass) in any room. Treating the room will tame its resonances and harmonics and allow whatever the speaker is "saying" to be heard more clearly.

As to tall speakers in short rooms, it depends on the speaker and it depends on what, if anything is done to the room. Comb filtering can result, even from short speakers in tall rooms, if there is sufficient energy and reflections cause cancellations at the listening position. Here too, I find this is a matter of set up and room treatment and is unrelated to speaker or room height. Further, certain types of speakers, like planar dipoles and line sources do not radiate much energy vertically (with planners, not much to the sides either - so that type starts off with 2/3 of the room excitement potential gone).

I would put any speaker I wanted in any given room. From there, just as with any speaker in any room, it is a matter of proper placement of speakers, listening position, and everything else in the room - and proper room treatment, ideally trapping the bass in the pressure zones, absorbing early reflections and diffusing later ones.

Best regards,

Barry

Soundkeeper Recordings

www.soundkeeperrecordings.wordpress.com

Barry Diament Audio

Excellent, thanks.

One clarification, if understanding correctly, large surface area woofers moving lots of air will excite room resonances more than small surface area woofers. If a large woofer is placed the same distance from a corner or boundary it will excite/energize the resonance more than a small woofer.Turning up the volume on either woofer would be expected to enegize the resonances also. Treatment of the room should work equally well in either circumstance, or turning down the volume in cases where room treatment is suboptimal.

Cheers

David

bdiament · March 2, 2015

Excellent, thanks.

One clarification, if understanding correctly, large surface area woofers moving lots of air will excite room resonances more than small surface area woofers. If a large woofer is placed the same distance from a corner or boundary it will excite/energize the resonance more than a small woofer.Turning up the volume on either woofer would be expected to enegize the resonances also. Treatment of the room should work equally well in either circumstance, or turning down the volume in cases where room treatment is suboptimal.

Cheers

David

Hi David,

It isn't the driver size that would determine the degree of room excitation for a given placement, it is the output level. The room has no way of knowing the size of the driver but it does respond proportionately to the sound level.

Similarly, room treatments don't know what kind of speakers or other sound generators are in a given room. Properly implemented, they will lower the "Q" of room modes (shortening decay time), prevent early reflections from reaching the listening position, and provide diffusion to later reflections.

Best regards,

Barry

Audiophile Neuroscience · March 2, 2015

Hi David,

It isn't the driver size that would determine the degree of room excitation for a given placement, it is the output level. The room has no way of knowing the size of the driver but it does respond proportionately to the sound level.

Similarly, room treatments don't know what kind of speakers or other sound generators are in a given room. Properly implemented, they will lower the "Q" of room modes (shortening decay time), prevent early reflections from reaching the listening position, and provide diffusion to later reflections.

Best regards,

Barry

Soundkeeper Recordings

www.soundkeeperrecordings.wordpress.com

Barry Diament Audio

Hi Barry

I thought it might be the volume of air being moved at a given Sound pressure level. Thanks for clearing that up

Cheers and keep well

David

flak · March 2, 2015

Hi Barry,

in my opinion your judgements, that are inclusive of the latest mixed-phase solutions like Dirac Live, Acourate and Audiolense, are inappropriate, the reasons I dare say so is that it appears from your previous posts that...

a- you have not listened to them

b- you have not measured them either

Many independent and knowledgeable forumers have taken the time and effort to measure the results and they are invariably positive, many many more have carefully listened at length and almost all of them have found substantial improvements.

Our approach is to have everybody try Dirac Live for free so that they can listen, measure and draw their conclusions by themselves without having to resort to self proclaimed "golden ears"

I have to add that even less advanced minimum-phase solutions (i.e. corrections as suggested by REW) have proven to give meaningful benefits, if judiciously and properly applied, and there is such a huge number of well informed testimonials and measurements that it is beyond doubt that some properly applied DSP correction can indeed be beneficial.

All of the above does not detract from the usefulness of passive treatment when feasible... what I find simply wrong and misleading is your taliban view that DSP/DRC processing is necessarily negative.

Flavio

bdiament · March 2, 2015

Hi Barry,
in my opinion your judgements, that are inclusive of the latest mixed-phase solutions like Dirac Live, Acourate and Audiolense, are inappropriate, the reasons I dare say so is that it appears from your previous posts that...

a- you have not listened to them

b- you have not measured them either...

Hi Flavio,

The OP asked a question and I reported my experience and my perspective. I'm sorry if that displeases you. Your nasty response doesn't put you in a good light. Since you feel free enough to make baseless accusations, I would to ask you to supply the evidence or offer an apology.

Please tell everyone how many times you have been at my studio (hint: zero) and how many times you have been present at any of the tests I've conducted (hint: zero). Yet you draw conclusions and make public statements about me based on nothing other than the fact that I have a different perspective from you. I'm afraid to say that is not very solid logic: conclusions based on zero data. And not very solid manners either.

You don't know what I have listened to and what I have not listened to. You don't know what I have measured and what I have not measured.

I've tried to maintain civility in these communications but I will confess I am losing patience with what seems to be a clear lack of confidence on your part and the increasing rudeness I sense in your posts to me.

If you are truly confident in your approach and your software, my feelings about it don't matter, do they?

I keep saying I will not argue and you keep coming back apparently seeking an argument or "proof" or whatever it is that will ease your mind.

Perhaps I have not been clear. I've tried to avoid being specific and not name your product and I will adhere to my principles, whether you like it or not my friend. But in my desire for you to understand why I won't reply to any continuation of this nonsense from you, dig this: I don't agree with your approach and I don't like your software.

How many times do I have to say that I'll be interested when your software can shorten the decay time of room modes, lowering their "Q", without altering the direct response from the loudspeakers?

I also resent your nasty accusations and will tell you they are not becoming of a professional. I've told you countless times now (and this will be the last) that I'm very glad your software has found happy users. I'm glad for you and I'm glad for them. It just isn't for me. I've already told you why (several times) but you don't seem to be able to let go. Let it go! Let us agree to disagree. And try to display sufficient confidence in your product and approach that my disagreement just doesn't matter.

Please re-read this post a few times because I'm not going to repeat myself anymore and I'm not going to respond to any further nastiness or baseless nonsense from you. I wish you happiness and I wish you continued success with your software. For the last time, it just isn't for me.

Best regards,

Barry