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Perceptual Effects of Room Reflections

North_Sky

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Ok, acoustic room treatments then.
Room EQ is for people who cannot afford room treatments...better than nothing.
 

JoachimStrobel

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I was actually making the same distinction but you are further confusing the issue by misunderstanding the reference to PA. It is useful to think of the audio system for recording and for amplifying the sound inside the theater as two separate but parallel systems even if they use the same mixer and mics. Also, let us not further confuse the use of amps and speakers required to get any sound out of an instrument like an electric guitar or the keyboards from the PA system to amplify the stage for the audience at a distance. You may mic the former to feed to the PA system but typically never mic the latter if you can help it, partly to avoid feedback if you are using the same system for recording and room PA (so there is no recording of a recording as you put it).

Think of those required electronics for some instruments as part of the instrument itself. Keeping these conceptual differences is key to understanding how audio engineering works for live performance or recording.

Talk of the PA system here is a red herring. Hypothetically, think of a live performance without ANY amplified audio inside the room that is good enough for an audience (other than any amps needed for electronic instruments which have no sound otherwise). Now, let us think of how to record it so it can be heard at home.

Basically, it boils down to how to mic it and how to mix it.

There are two different issues - how to capture the quality of the sound and ambience and how to represent the stage in terms of locating the listener relative to the stage. These are two separate issues. These have nothing to do with whether there was a PA system (for stage amplification different from instrument required transducers) in the location or not. This must be clearly understood before proceeding further.

Any mic positioning for recording is at best an approximation to the live performance. But you are not going to get a recording without mics. So, a whole part of audio engineering is to determine the position of the mics so that it captures the sound quality of various instruments and/or vocals. Think of this as just raw data before mixing. You can also mic to capture the ambience to input into the mix. So far, it has nothing to do with how many channels in recording output. These are all independent cables coming into the mixer from various positions and have no relation to the speaker channels at home yet. As I have mentioned, there are limitations to capturing the timbre and ambience of a performance perfectly but that is a given. These have nothing to do with if there was a PA system in the theater or not.

Now, once you have the raw feeds coming in, there is the question of how to mix it for the final output into a recording whether stereo, or multi-channel. But regardless of the latter, there was a discussion earlier of whether the position of the listener being represented in the recording is as being located in the audience or in the midst of the performers. This should not be confused with the other issue of quality of sound capture. You can use the exact same mic positioning and their raw feeds that gives the best quality you can get to mix it for either of those listener positions. You can do it in stereo or multi-channel for either.

My first point was that mixing the output from the perspective of a listener in the middle of the performance has no basis in reality of a listener being in the middle of a stage in a live performance. The latter in live performance is not good because of lack of balance between instruments on stage (with some exceptions as I have mentioned). So, you can create a virtual world from the raw feeds coming in and mix it as if the sounds were coming from all around you rather than in front of you. This is what some of the multi-channel SACDs do when they remix from original independent tracks even of a live performance. The goal here is never one of capturing the actual performance in terms of positioning even for a live performance for reasons mentioned above. Conceptually, they are not very different from some of the post-processing surround modes that try to approximate it from stere recording outputs.

Second, there is a misunderstanding that recording from an audience location perspective is to be done by recording what comes out of the PA system. In general, this is not true (with some exceptions for ambience or in budget/amateur gigs). It isn’t. It is created by mixing the same incoming mic feeds that are fed to the PA system if one exists. In budget/amateur settings, the two mixes might be the same but in most professional settings, it isn’t. The PA system isn’t typically just 2 speakers. The PA mixing goal here is to amplify the sound so that ideally it is as if the stage is playing louder to be heard in the audience NOT that the saxophone is moved to the left speaker. This is achieved via a combination of strategically placed speakers and mixing feeds in right proportions between them.

The mixing for recorded output from the audience position is conceptually different although it has the same goal as the PA system - to make the stage be heard as a stage in front of you. Just to be clear again, this is typically not done by mics in front of the PA system to capture what the audience is hearing except in budget/amateur productions.

If both are done correctly and professionally, the image of the stage projected with PA amplification in the performance is the same as the stage projected by the recording at home for a listener at the center of the audience (or wherever the mixing engineer’s reference point is), in reality a decent approximation. So from that perspective, it is capturing the live event as heard in the audience (but not by placing mics in front of the PA system, I keep repeating this because this seems to be misunderstood).

Multi-channel output capability can enhance either of the listening position reference points. In terms of the virtual world of being on stage to listen, it is almost a necessity. In terms of the reference point of being in the audience, it can be used to enhance ambience and the “live nature” in terms of audience presence if that is required.
Thanks for the good explanation. I may have added a bit confusion with my original post: I simply wanted to say how good and natural instruments sound in any room and how I perceive the addition of direct sound (by a close microphone and loudspeaker) as degrading the sound experience. And I am not sure I understand the requirement of room treatment considering that I do not see room treatments in many small Jazz venues (or else).

The answers make me iterate on two issues:
  1. Given that the reproduction of the concert hall/room is difficult, is it then then not better to concentrate on “on stage” mixings? Where the listener is surrounded by instruments, be it a real or artificial placement. This is then a new, non-comparable to live, recording. The loudspeakers carry less instruments and give them more weight.
  2. And … this touches on the room curve too. I am still not sure (even after many posts) how a mix of traces containing signals from the audience-distance, with dispersion and reflections reducing higher frequencies, and traces with near-instruments microphones are finally mixed so that me as a consumer can add another room (either natural or Eqed) curve on top. The issue seems simpler with the “surrounded by instrument” mix, where the close-microphone trace can stay as is and the room curve will be added by my system (creating a “surrounded by instruments” field with dispersion and little reflections…)
 

audimus

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Given that the reproduction of the concert hall/room is difficult, is it then then not better to concentrate on “on stage” mixings? Where the listener is surrounded by instruments, be it a real or artificial placement. This is then a new, non-comparable to live, recording. The loudspeakers carry less instruments and give them more weight.
Not necessarily. Getting a room feel is very easy and most hall-effect type post-processing modes do this fairly well. You can even simulate small room, large room, etc. The difficulty is not in the mixing for a location. It is placing the right type of mics in the right locations to capture the acoustic instruments and voices without getting affected by other instruments in the proximity, etc. Obviously, much easier for electric instruments since you already have the electrical signal. You have that problem regardless of what mixing you do. But you are correct in the sense that more channels you mix for, the easier it is for instrument separation. But many recordings done this way sound bad/artificial.

The main reason is that the mixing engineer has no control over how the multi-channel speakers are placed at home. Most common are HT configurations with side or rear surrounds. This configuration is actually bad for an immersive sound stage because in most home setups designed for HT, the distance between the mains and surrounds are too large and leave a huge gap say between L and SL or RL. Not a concern for HT because of the purpose for which the surrounds are used are different, not in equal terms with the mains and center. Moreover, the mixing engineer has no control over what this gap is since it varies a lot from home to home.

Some people who use multi-channel for only music place the “surrounds” at the sides ahead of the listening position in a way that is basically a semi wrap but in front. That has the advantage of wrapping the widened stage and the advantage of separating out the instruments without the spatial gaps of a HT set up. But this is not a common/standard enough configuration for a mixing engineer to use as a reference to mix for.

And … this touches on the room curve too. I am still not sure (even after many posts) how a mix of traces containing signals from the audience-distance, with dispersion and reflections reducing higher frequencies, and traces with near-instruments microphones are finally mixed so that me as a consumer can add another room (either natural or Eqed) curve on top. The issue seems simpler with the “surrounded by instrument” mix, where the close-microphone trace can stay as is and the room curve will be added by my system (creating a “surrounded by instruments” field with dispersion and little reflections…)
There might be a misunderstanding of what a room curve is in the context of room correction. A room curve is not a room simulator of where the recording is. It is a term for a particular tonal balance of any speaker, typically a bit boosted in the lows and tapering down towards the high end to compensate for the effect the listening room on the relative hearing across the spectrum, in short to neutralize the listening room characteristics which typically absorbs more of the lows than the highs.

What you are perhaps referring to is the room effect type of DSP processing added to the source content to create a performance room like atmosphere with reverbs and echos and delays. This is obtained by switching on that mode in your integrated amp or AVR or pre/pro with a DSP. Of course, a mixing engineer cannot assume that any such thing exists at the consumer’s end so if they think it necessary they add their own room effect. If they don’t, some people prefer listening to their music with a room effect turned on in their audio system but not all do.
 

JoachimStrobel

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Not necessarily. Getting a room feel is very easy and most hall-effect type post-processing modes do this fairly well. You can even simulate small room, large room, etc. The difficulty is not in the mixing for a location. It is placing the right type of mics in the right locations to capture the acoustic instruments and voices without getting affected by other instruments in the proximity, etc. Obviously, much easier for electric instruments since you already have the electrical signal. You have that problem regardless of what mixing you do. But you are correct in the sense that more channels you mix for, the easier it is for instrument separation. But many recordings done this way sound bad/artificial.

The main reason is that the mixing engineer has no control over how the multi-channel speakers are placed at home. Most common are HT configurations with side or rear surrounds. This configuration is actually bad for an immersive sound stage because in most home setups designed for HT, the distance between the mains and surrounds are too large and leave a huge gap say between L and SL or RL. Not a concern for HT because of the purpose for which the surrounds are used are different, not in equal terms with the mains and center. Moreover, the mixing engineer has no control over what this gap is since it varies a lot from home to home.

Some people who use multi-channel for only music place the “surrounds” at the sides ahead of the listening position in a way that is basically a semi wrap but in front. That has the advantage of wrapping the widened stage and the advantage of separating out the instruments without the spatial gaps of a HT set up. But this is not a common/standard enough configuration for a mixing engineer to use as a reference to mix for.


There might be a misunderstanding of what a room curve is in the context of room correction. A room curve is not a room simulator of where the recording is. It is a term for a particular tonal balance of any speaker, typically a bit boosted in the lows and tapering down towards the high end to compensate for the effect the listening room on the relative hearing across the spectrum, in short to neutralize the listening room characteristics which typically absorbs more of the lows than the highs.

What you are perhaps referring to is the room effect type of DSP processing added to the source content to create a performance room like atmosphere with reverbs and echos and delays. This is obtained by switching on that mode in your integrated amp or AVR or pre/pro with a DSP. Of course, a mixing engineer cannot assume that any such thing exists at the consumer’s end so if they think it necessary they add their own room effect. If they don’t, some people prefer listening to their music with a room effect turned on in their audio system but not all do.
Many thanks for the deep answer.
Room curve: No, I mean the “tonal balance curve”.
Well designed loudspeakers have a smooth off-axes “decay” that produces the said tonal balance to offset small room’s deficiencies. I call this the natural room curve.
When using an EQ process for the full frequency range, for whatever reasons, one has to dial in a target curve. That should not be a flat target as then the natural fall-off is taken out. This natural fall-off is actually a convolution of the fall-off in a reflection-free room and the actual room itself. Without having that zero-room reflection fall-off, which some manufactures do publish, one can not design the perfect artificial room curve but takes a standard one - like the one Toole has published.
An instrument played in a room will show a similar fall-off. Moving closer to the instrument will make it sound brighter. That can be tried by playing a grand piano, opening it and removing the music sheet stand too.
A microphone placed close to instruments will record that, and when played back in my listening room, my room curve (natural or artificial) will kick in. If the audio engineer added one too, then I and up with a double room curve (and some people said, this is when, in old times, on reached for the amplifier’s treble adjustment).
So, I am not too sure how this handled in general.
But it gets more complicated when near field and far field (audience distance) microphones are mixed, as the audience microphones will have recorded the said frequency dispersion.

And then, with immersive Mch, with all instruments recorded with near field microphones, things should be easier as no far field microphone gets in the way, and my room curve then compensates only for my room, probably making the instruments sound as they were 10 meter away from me. Unless the audio engineer added a room curve already to compensate for the bright sound he hears from his pure direct sound monitoring setup...
 

audimus

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And then, with immersive Mch, with all instruments recorded with near field microphones, things should be easier as no far field microphone gets in the way, and my room curve then compensates only for my room, probably making the instruments sound as they were 10 meter away from me. Unless the audio engineer added a room curve already to compensate for the bright sound he hears from his pure direct sound monitoring setup...
I am not sure I understand the above, perhaps I am missing something. The mic positioning is designed to not get any of the performance room deficiencies for recording instruments or vocals. They all tend to be highly directional or often directly attached to instruments so to avoid picking up any other instruments let alone any effect of the room where the performance is. There might be a separate sampling of the room ambience if they want to get the live hall effect but that is a specific mic setup to pick up exactly what they need. So they are all “near field” effectively. And this applies whether the final mix is to put the stage in front (this does not mean they put the mics far away at the listener’s position) or locate the listener in the middle of the performance or how many channels it is recorded for. The perception of relative distance from instruments is based on the volume balance between them and the direction based on the proportions spread to channels during mixing.

Audio engineers can and often eq while mixing to get the right tone balance between the various tracks just as they do with relative volumes. And they get the overall balance with a studio reference setup that is treated to be more or less neutral or some proprietary reference, so they don’t need to compensate with a room curve, just get the tonal balance desired by the producer/artiste in that reference. The goal of a home system is to hear that same balance by reproducing it as faithfully as possible and compensating for your listening room if necessary never for anything in the recording. If your room is perfect and your audio system perfectly transparent, there is no room curve necessary for what is in the recording.

So your room eq does not need to compensate for anything other than your room in any scenario.

Unless it is a boot leg tape from someone in the live performance audience which is unlikely to be a multi channel anyway. :)
 

Lifer

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Hello,
First of all, thank you for all the knowledge you share with the community.

I write this because after reading this post I am a bit lost. I just moved into a new apartment with quite a small living room according to US standard (17*14ft). I was going to treat the early reflections to approach an RFZ but now I am not so sure it's a good idea.

If early reflections are a good thing and you should not treat them, then how do you acoustically treat a room ?
Should I still treat the floor, ceiling, front and rear walls and just leave the lateral walls untreated ? Should I treat reflections with >25ms delay and leave the early ones ? Is it pointless to treat at all acoustically and I should only use Subs & active EQ ?

Thank you very much in advance for your help
 

Ethan Winer

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I assure you that treating early reflections is a Good Thing in all rooms where music is played:

Early Reflections

But there's more to room treatment than just absorbing reflections. You also need bass traps. This short article explains what acoustic treatment does, and why it's more important for quality sound than almost anything else:

Acoustic Basics

This explains even more, if you're really interested:

Bass Trap Myths
 

eliash

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I assure you that treating early reflections is a Good Thing in all rooms where music is played:

Early Reflections

But there's more to room treatment than just absorbing reflections. You also need bass traps. This short article explains what acoustic treatment does, and why it's more important for quality sound than almost anything else:

Acoustic Basics

This explains even more, if you're really interested:

Bass Trap Myths

Your "Early Reflections" article swiftly uncovers the reasons for the painful discovery process I´ve gone through for several years to get rid of (personally) perceived annoying distortion, basically emerging from sidewall and in my case also tilted ceiling reflections!
It could be that, as you wrote, aging ears effects, or maybe also personal advances in listening capabilities, reveal them only later in life...
 
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Your "Early Reflections" article swiftly uncovers the reasons for the painful discovery process I´ve gone through for several years to get rid of (personally) perceived annoying distortion, basically emerging from sidewall and in my case also tilted ceiling reflections!
It could be that, as you wrote, aging ears effects, or maybe also personal advances in listening capabilities, reveal them only later in life...
could you please clarify how did that annoying distortion sound?
 

eliash

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could you please clarify how did that annoying distortion sound?
Actually it sounded a bit like intermodulation, especially arising at higher frequencies starting at the upper voice range and its overtones. As I wrote, it could be that the ears resolution to automatically differentiate between familiar and suppress unfamiliar (artificially generated, e.g. by the early reflections) spectral content gets lost over time.
Another contributing factor was also vibrating speaker enclosures, accelerated by the 2 woofers, even though mathematics (Doppler-IMD around -30dB???) does not verify this in such quantity. Anyway, measures on both causes yielded finally salvation (I am really serious about the term "salvation", since this effect caused a lot of grief to me, over several years!).
 
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Sal1950

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I write this because after reading this post I am a bit lost. I just moved into a new apartment with quite a small living room according to US standard (17*14ft).
Outsiders must think everyone in the US lives in places like the Trump mansion.
We're not all rich here you know, far from it.
The vast majority are middle class working folks who live in homes with living rooms that approximate yours or even smaller.
Some photos of the homes I live/lived in.
IMG_0564.jpeg

2640-42 Jackson.png
Armitage_v1.jpg
clinton.png
 

amirm

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If early reflections are a good thing and you should not treat them, then how do you acoustically treat a room ?
If this is a multipurpose room full of furnishings and such, there is no need to acoustically treat a room. Acoustically treating a room is most necessary for empty, dedicated rooms.

If your room has a lot of hard surfaces without much damping material, then yes, putting a thick carpet on the floor is a good start.
 

Ethan Winer

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If this is a multipurpose room full of furnishings and such, there is no need to acoustically treat a room. Acoustically treating a room is most necessary for empty, dedicated rooms. If your room has a lot of hard surfaces without much damping material, then yes, putting a thick carpet on the floor is a good start.
I'm really surprised to hear you say that, Amir. Have you never seen the response and ringing in an untreated room? My Early Reflections article above shows how terribly skewed mids and highs are when the specific reflection points aren't treated. And carpet addresses only one of those four locations. But bass problems are at least as damaging to sound quality. This is a typical bass response with and without bass traps in a room the size Lifer has:

Bass Trap Response.png


And this shows the ringing (decay times) that accompany each peak:

Bass Trap Ringing.gif
 

krabapple

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I assure you that treating early reflections is a Good Thing in all rooms where music is played:

As I am sure you are aware, that;s one perspective. Another is derived from the research Dr. Floyd Toole often cites: that under conditions where loudspeakers are well behaved both on and off axis, early reflections can sound pleasant to many listeners by increasing ASW (apparent source width) and 'envelopment'.
 

krabapple

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It is of course difficult to test the subjective effect of /preference for physical room treatments properly -- i.e., double blind tests. In the end, what matters is what's audible; not all measurable things matter, and audible things do not all matter equally.
 

Ethan Winer

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Dr. Floyd Toole often cites: that under conditions where loudspeakers are well behaved both on and off axis, early reflections can sound pleasant to many listeners by increasing ASW (apparent source width) and 'envelopment'.
Yes, unsophisticated listeners who aren't used to the clarity of reflection free listening might find the improvement unfamiliar and even jarring at first. But in the world of audio professionals - people who create and listen to music for a living - early reflections are not considered beneficial. I have visits from people who are both professional and lay, and everyone universally comments on the amazing clarity and overall excellent sound of my living room system which is very well treated.

Look, people like what they like, and nobody can say they're wrong. If Floyd Toole prefers boomy bass and comb filtering, that's his preference. But people who at first prefer "room sound" often come around once they've become acclimated to the improved sound of no reflections.
 

krabapple

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If you were familiar with Toole's writings, you'd know he's written about the disparities between preferences of audio engineers versus consumers. And that even within audio professions, there is diversity:

e.g.
https://www.audioholics.com/room-ac...ons-human-adaptation/what-do-listeners-prefer
"A recent study reported that mixers preferred attenuated lateral reflections, but mastering engineers preferred a more normally reflective room. In both cases, results were different with different songs. (Tervq, et al. JAES, 2014)."


You'd also know he calls reflection treatment 'optional'; that there is no single 'right' way' that fits all situations. As for comb filtering, he cites research showing that in most cases it's not even an audible problem for listening enjoyment.

You'd also know that the listeners in the test he cites were hardly all 'unsophisticated'. They were also screened for actually having intact hearing, which often older people (including Toole himself) can no longer claim. Which btw has an impact on preference for lateral reflections.

You're also wrong about Toole and 'boomy bass'...he's got probably the most sophisticated multi-subwoofer 'room correction' system available, running in his home system. Harman, his former employer, has done some of the most fundamental and often-cited research on subwoofers and rooms, after all.

Good audio science involves taking the proper before/after measurements *and* running bias-controlled listening tests. There's undeniably a distinct lack of the latter as regards physical room treatments (and too little regarding software approaches as well).

I would expect that on something called 'Audio Science Review', anecdotes don't rate. I also highly doubt that anyone would like listening in a room with 'no reflections'.
 

amirm

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I'm really surprised to hear you say that, Amir. Have you never seen the response and ringing in an untreated room?
Not at frequencies above transition. You are showing low frequencies in your graphs which are best dealt with using EQ. Absorption at low frequencies require very deep porous abosorbers due to large wavelengths that we are dealing with. Your graphs still show chewed up response even with the bass traps added. EQ is mandatory for smooth response. There is no getting around it.

Here is a simulation of a 4 inch absorber (1.0 means 100% absorption):
1577489033741.png


As we see, there is hardly any absorption at 100 Hz. It becomes most effective past 400 Hz and by then, most of your bass problems/resonances are behind you.
 

ernestcarl

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I would expect that on something called 'Audio Science Review', anecdotes don't rate. I also highly doubt that anyone would like listening in a room with 'no reflections'.
If you read Ethan's whole post again, he clearly meant 'early reflections'. I have mixed feeling about this topic, but I think some kind of room treatment is always beneficial. With a dry room, you can always artificially add reverb.
 
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