Announcement

Collapse

HUG - here for all audio enthusiasts

Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings sub-forum is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.

The Moderators' decision is final in all matters regarding what appears here. That said, very few Posts are rejected. HUG Moderation individually spell and layout checks Posts for clarity but due to the workload, Posts in the Subjective Soundings area, from Oct. 2016 will not be. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

That's it! Enjoy!

{Updated Nov. 2016A}
See more
See less

Adjusting Room sound using material damping methods (not DSP)

Collapse
This is a sticky topic.
X
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Interpreting absorption coefficient data?

    Originally posted by A.S. View Post
    ......so a number greater than 1.0 would seemingly not be possible. If the measurements were comparative, with one data set normalised then a figure greater than 1.0 (100%) would be possible comparatively. So I'm mystified - can anyone explain this?....
    I was asking the same question when I was looking at Roxul rockwool specifications which I used for my room. The absorption rate value is given for x surface area. So at any given frequencies it is measured based on the total surface area of the absorption material. OTOH, for some frequencies the total required area of absorption material needed to achieve 0 reflection will be lesser than the standard "x" area . In that case the value is stated to be more than 1.

    ST

    Comment


    • Dry recording - a long excerpt

      I think you have drawn a conclusion that you prefer the dry recording based an a very short clip. I've made a longer clip for you, below. Even on this dry recording (actually recorded under quasi-anechoic conditions) the string tone sounds OK. It seems to change less in tone than other instruments when we strip-out the reverberation. But towards the end listen carefully to the woodwind - horribly dull and unnatural - and also listen to the airless, absence of reverberation between the musical pulses (I don't know what the correct musical term is). The last two seconds are interesting - you can clearly hear the body resonance decaying from what I assume is the cello. We wouldn't normally be able to hear that against the more dominant reverberation.

      [Clip #4]

      BTW, on the previous three clips, the levels are about the same: but the perceived loudness is not as you found. Reverberation adds loudness.

      I don't believe for a moment that you really like this clip unless you are a professional musician earning your living in the orchestra pit under the stage in a concert hall where this dry, reverberation-free sound would seem quite normal to you!
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK

      Comment


      • Thank god! I am still normal.

        Originally posted by A.S. View Post
        .... I don't believe for a moment that you really like this clip unless you are an professional musician earning your living in the orchestra pit under the stage in a concert hall where this dry, reverberation-free sound would seem quite normal to you!
        Thanks for the longer clip. Yes, this is dry and the youtube is not my liking, either. But in the earlier post, in the second clips what sounded like the sound of "running tap" is audible more clearly compared to the first one at the same volume setting. Maybe, that's why I concluded the second one sounded a tad louder than the first. And, yes the woodwind(?) sounded bit unnatural.

        ST
        ______________________________________
        p.s. BTW, I also find Harbeth CD recording to be dry in the video clips but the flash sample was good.

        Comment


        • Adding ambience (reverb) to the dry recording

          Leading up to the treatment of the listening room, let's take that dry recording and enhance it to make it sound more like what we'd hear in the concert hall. First remember what the dry reverberation-free sound was like here:

          [Clip #2 again] (Dry-sound reference clip)


          Now we added-in reverberation and remove the direct sound because this is more representative of what you would actually hear in the hall, way back from the stage.

          [Clip #5] (Some artificial reverb added)

          Now to my ears this is beginning to sound more like the real thing. Notice that there are no longer dry gaps between the notes and pauses - they are filled with an evenly decaying echo. And now that last two-seconds of belly sound is obscured under the general reverberation. N.B. this resulting mix is entirely synthetic. There was no concert hall. The performance was recorded under almost anechoic conditions. The reverberation effect is achieved by taking the dry direct sound and mathematically delaying it sample by sample and adding it back to the original dry sound in a controlled way. I have total flexibility over how much reverberation to add, and I can synthetically change the size of the fake hall, and the absorption of its walls.

          The reverberation in the above clip sounded characterless - that is, there no tone or frequency or signature that draws attention to itself in the reverberation. We absolutely do not want to be recording (or listening) in a space that has a strong sonic signature because a certain combination of musical notes will excite the hall's characteristic signature-sound and it will be picked-up by the microphones. Here is another faked hall, using the exact same dry source and feeding it through the processor. In this example, I've told the processor to create a maths model of the hall where some surfaces have solid, brick surfaces (with low absorption). This imparts a sonic over-brightness or hardness especially in the upper frequencies here:

          [Clip #6] (Different artificial reverb added)

          Again, this is the problem we face at home. Some, well controlled, even, characterless reverberation in our listening room is generally acceptable: the problems is when the reverberation takes on a characteristic 'twang' which is excited by certain notes or instruments. In this example, the string tone is now exceedingly gritty and bright. Listening becomes unbearable once our ears are pre-sensitised to the effect.
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK

          Comment


          • Why concert hall RT?

            I would appreciate if you could explain why you are choosing to concert hall sound as a reference? IF I could record exactly what I hear in the concert hall and were to play the same recording in my listening room would it still sound identical? Or will my own room reverberation time add colouration to the recording? Should I then reduce the reverberation time of the concert hall recording to make up for my room's reverberation time?

            To my understanding, reverberation time is room size dependent. If for a small room the ideal RT is around 0.35s then for a concert hall it could be 2s. This is where I am always confused because if we were to listen to live recording then we should be listening in anechoic chamber because the live recording already captured the reverberation time of its venue.

            Taking Alan's post #25 sample, what would be the correct reverberation time need to be added to the recording if it were to be played in a small room and in another room 10 times the size?

            Even though, I started my room RT at 0.28s and now have moved up to about 0.35s which is more realistic and natural I still do not know how the recording engineer decides how much reverberation time to be added to a recording given the fact he is unable to tell how big the listener's room is going to be and why most recording sounds right in my room.

            ST

            Comment


            • Originally posted by STHLS5 View Post
              I would appreciate if you could explain why you are choosing to concert hall sound as a reference? ... To my understanding, reverberation time is room size dependent. ... I still do not know how the recording engineer decides how much reverberation time to be added to a recording given the fact he is unable to tell how big the listener's room is going to be and why most recording sounds right in my room.ST
              Back a few steps then and a summary. You really need time to walk around this - and that can take days or longer; it's not possible to distil a useful foundation of the subject in just a few posts. Please don't rush yourself. These things take time. I pick my words and examples very carefully with an end-point in mind and need a little time and space to work it up, step by step. OK, back a few steps then.

              As I stated a few post ago:

              The basic truth of high fidelity sound reproduction in the home is that the acoustic signature of the listening room is the final link the the reproduction chain
              and of the instrument in the studio reproduced by a speaker in the home ...

              A box in a box in a box in a box. No surprise then that each box will have a modifying effect on the preceding signal.
              So, it hardly matters whether we focus on the recording studio or hall or the reproduction room - the acoustic problems are common. I also said:

              We at home have no influence over the studio (or hall) that the recording was made in, so that leaves only the listening room as within our capability to modify...
              Then I went on to say ...

              I can give an example of just how much the room contributes if we make a recording of an orchestra in a concert hall and then transport the orchestra to an anechoic chamber and re-record them there. Same orchestra, same instruments, same microphones; the only difference is the complete absence of echoes in the anechoic chamber. So the difference between these recordings is solely that of the contribution of the room.
              Now, from a point of practical demonstration, given that the issues that bedevil the recording venue are conceptually the same as those of the listening room (echoes, standing waves, surface absorption differences and the rest) it's much easier for me to demonstrate with sound clips of the recording room rather than visit your home and make technical measurements there - if we agree that conceptually the acoustic problems are the same. Agree? I assume that we do but if we don't tell me.

              OK, then we need to assure ourselves that a dry recording is the sound from the instruments directly to the microphone taking the shortest possible path and that there are no room characteristics (reverb, echoes etc. etc.) at all in that dry sound. Then we can artificially add-in the 'room sound' and create a concert-hall like sound from what had no hall acoustic at all. In other words, we have taken those musicians recorded outside in a field (or an anechoic chamber) and placed them in a hall of our choosing at a whim by adjusting the digital 'hall creator tool'. See screen attached.

              Then we're ready to attack the central point we've been working towards. As I said ....

              The reverberation in the above clip sounded characterless - that is, there no tone or frequency or signature that draws attention to itself in the reverberation. We absolutely do not want to be recording (or listening) in a space that has a strong sonic signature because a certain combination of musical notes will excite the hall's characteristic signature-sound and it will be picked-up by the microphones. Here is another faked hall, using the exact same dry source and feeding it through the processor. In this example, I've told the processor to create a maths model of the hall where some surfaces have solid, brick surfaces (with low absorption). This imparts a sonic over-brightness or hardness especially in the upper frequencies here:

              Again, this is the problem we face at home. Some, well controlled, even, characterless reverberation in our listening room is generally acceptable: the problems is when the reverberation takes on a characteristic 'twang' which is excited by certain notes or instruments. In this example, the string tone is now exceedingly gritty and bright. Listening becomes unbearable once our ears are pre-sensitised to the effect.
              The essence of this is humans have adapted to the sonic signature of our voice (and much later, music) in confined spaces, initially caves and now rooms. We know how a voice or instrument sounds in the absence of a strong room acoustic and provided that there are no dominant acoustic issues (such as the hardness or twang in the above clip) we are completely able to listen in comfort even on relatively low-fi equipment. The problem is not therefore whether you select 0.2mS or 0.4mS average decay time for your listening room - that really is a matter of your choice as to whether you prefer a dryer or more live listening environment - the problem is when certain echoes and frequencies fall outside that average decay time. These frequency bands (or echoes) are really irritating to listen to, akin to a constant drone and no classical western music would have such a character. Hence the subconscious needles to conscious with the constant reminder 'something artificial about this sound .... evolution has not prepared me for this ... is it a thereat? Fight or flight?'. And the listening session is undertaken in a state of some subconscious anxiety.

              So where are we at? I hope that I've illustrated that the recording room and the listening room both have the potential to superimpose their character on the recording. The problem is not global reverberation - providing that it has an even decay - the problem is almost always the 'hot' sonic bands that for some acoustic reason or another stick out like sore thumbs over the music. And to answer your question, why take the hall as the reference: a well designed hall with an even, characterless decay is the best venue to listen to classical music in, and has been for hundreds of years because as we've seen, it adds loudness and presence, and carries the sound through the audience.

              And what makes a truly great acoustic space with an even, characterless decay? Accident or design? Both.
              Attached Files
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • Room sound perference?

                An observation: many years ago, I moved from one home to another. In the place I moved from, I had an almost anechoic listening room; and while I was quite certain that the room was contributing next to nothing to the sound, I found that in my new place, which had a real nice balance of reflective and absorbtive surfaces, I preferred this sound environment immensely to the other.

                Just a thought on the subject...

                Comment


                • Educational and interesting - thanks

                  Alan,

                  Once again, a great post that is interesting as well as very educational. You support is sincerely appreciated.

                  John

                  Comment


                  • Loudness

                    Originally posted by A.S. View Post
                    ....... BTW, on the previous three clips, the levels are about the same: but the perceived loudness is not as you found. Reverberation adds
                    loudness.....
                    Thank you very much for the last post. I need more time to digest them. Meanwhile, I still need guidance from you regarding the post quoted above. Please allow me to digress a bit.

                    You mentioned reverberation adds loudness. As I have mentioned earlier, I found that the dry recording sounded louder and better (which may be due to the fact more details heard). However, I am unable to move forward as for someone who has none whatsoever knowledge about reverberation time and recordings I depend on my ears to judge what sound is correct and not.

                    Please understand that culturally I am from a very different background and orchestra music is not something I am accustomed to. The truth is I am the first generation in my family line to be exposed to the live orchestra sound and music. Culturally, for at least 2000 years my generations (race/ethnic) have been exposed to a different musical environment almost on daily basis where the musical piece and instruments have remained unchanged for the last 2000 years. It is difficult to relate to what you are expressing because I have never heard most of the instruments individually. So for what sounds unnatural woodwind to you maybe perfectly alright for me so long the pitch is correct. Therefore, I request that you bear with me for having a different perception with your samples.

                    The samples are important to me because if I can't grasp the intended message in the samples than the subsequent discussions become incomprehensible to me.

                    I have extracted your samples and run a spectrogram analysis. In the attached charts, you could see that there were more intensity of loudness in the dry recording Co-incidentally the highest amplitude in loudness is found in dry recording Please see chart B. By comparing Chart A and B and also the spectrogram analysis the first 5 seconds is definitely louder in dry recording.

                    So my question is, how can a dry recording without reverberation is louder and intense than with the wet recording?

                    ST

                    Comment


                    • Interesting about cultural experience. We need to cover that in more detail later.

                      First, I did not say that I had made any serious effort to equalise the levels of these clips. I just cranked up the loudness, clip by clip, until I didn't have to fiddle with the volume control on my PC speakers per-track. As I recall, the VU meters peaked about the same and as far as I was concerned that was good enough. The loudness of these clips is not at all the issue and is taking the discussion off into another direction. To exactly equalise the perceived loudness of these clips requires a day's effort, much experimentation and is, as far as this goes, irrelevant. So can we please just ignore that?

                      Dead stop again.

                      Q: What is Alan trying to convey in this thread?
                      A: That the box in which the recording is made (the studio, hall) and the listening room have similar acoustic issues.

                      Q: What does that imply?
                      A: It implies that if we understand one, we may be able to understand the other.

                      Q: Why has Alan made examples of dry and wet recordings? How is that relevant to the listening room as opposed to the recording room?
                      A: He can't visit your listening rooms to make measurements (he would if he could). And dry, reverberation-free recordings are available to him from a CD. So it's much easier to give examples of acoustic environmental issues using these studio clips.

                      Q: Is reverberation necessarily a bad thing in the recording studio or concert hall?
                      A: Absolutely not. The problem is not (usually) the amount of reverberation (within reason), the acoustic problem is the quality of the reverberation. Some of the most revered halls have a reverberation time of several seconds! For hundreds of years western music has been performed in churches and other large spaces with a lively acoustic. The most revered spaces have a very even 'sweet' reverberation as this gives air to the performance, and loudness.

                      Q: About the home listening room: should this be a dry or wet acoustic?
                      A: Neither. It should be a comfortable and realistic balance between these extremes.

                      Q: Is it advisable to kill all reverberation in the home listing environment by lagging the walls with thick acoustic treatment?
                      A: That may well destroy the natural balance in music. It would be over-kill. We are accustomed to and expect a certain amount of reverb or echo when listing at home as we did when living in caves.

                      Q: So what is the real issue with listening rooms? Why do some people struggle to get a good sound?
                      A: We're coming to that. As Alan stresses, the problem is (usually) not the quantity of reverberation or wetness in the room, it's the quality of the reverberation where the problems lie. When the reverberant echoes take on an acoustic character they mix together with the new notes and the sound becomes colored and irritating. He's demonstrated this in the clip, again here:

                      [Clip # 1 again] (Good quality reverberation)

                      [Clip # 6 again] (Approx. same quantity of reverberation, different quality of reverberation - this track is somewhat louder to emphasise the point)

                      Hopefully you can hear that there is a distinct character to the acoustic space around the performers in the above clip - the longer you listen the more obvious it becomes until you can emulate the character by making "awwwww" sounds with your open mouth i.e. the character has a distinct pitch (or multiple pitches)

                      OK. Please confirm that for these core issues we can proceed.
                      Alan A. Shaw
                      Designer, owner
                      Harbeth Audio UK

                      Comment


                      • One tiny word ... one giant leap?

                        None of us have all the answers. Almost everything I've gleaned over the years has been the result of self-curiosity and private study plus a great big dollop of trial and error.

                        Now, I'm not sure if you spotted the giant mental stride we made in my last post. I very subtly sneaked in a hugely important concept in the penultimate line of my post. I introduced the word pitch. I actually said ....

                        ...the longer you listen the more obvious it becomes until you can emulate the character by making "awwwww" sounds with your open mouth i.e. the character has a distinct pitch (or multiple pitches).
                        Did you see it? Can you see how hugely relevant this seemingly innocuous little word is? I'll give you a clue - and I want you to dwell on this for a few hours before you feel tempted to reply! ... we're talking about reverberation not music.

                        I'm going outside to dig-out the car from the snow and I won't be around for a few hours myself so take your time! This is really at the heart of the entire subject.
                        Alan A. Shaw
                        Designer, owner
                        Harbeth Audio UK

                        Comment


                        • Looking for "awwwww"

                          Originally posted by A.S.;12181....
                          Did you see it? Can you see how hugely relevant this seemingly innocuous little word is? I'll give you a clue - and I want you to dwell on this for a few hours before you feel tempted to reply! ... we're talking about [I
                          reverberation[/I] not music.

                          I'm going outside to dig-out the car from the snow and I won't be around for a few hours myself so take your time! This is really at the heart of the entire subject.

                          Well...it is 9.41pm here. I have made up my mind the first time I heard the sound that the first recording sounded right. Did I hear the "awwwwww"? Well... I heard musical notes hangover. Something that fills the gaps. In spite repeatedly listening for what you are attempting to describe as 'awwww" I am unable to say whether I heard "awwwww" or "ahhhhhh". Is it "awwww" or something that I describe as noise remains unknown. Please pardon me if I can't describe the "awwwww" correctly. Remember I am unable even to tell if Heather said "Right" or "Bright!" or...

                          Just to be doubly sure that Alan is not playing any tricks, I got my 7 and 11 year old trusted guinea pigs (my children) to go through his clips. My 11 year son preferred the first clip. He could describe the sound better than me that he was able to say the noise similar to "awwww". So too my 7 year daughter though she can't describe what's she was hearing but preferred clip 1. What is important to note here, generally, human behaviour would prefer the loudest to be better. As a speaker designer, I am sure you are aware of what I am trying to convey here. So we are on the right track even though how I interpret the sound quality may differ.

                          I am sure other members would be able to convey their opinion better as I am with the least exposure to western music even compared to my "audiophile" friend over here. However, in terms of reverberation I am able to accurately identify what should be right so long it doesn't affect the clarity of each notes or instruments. But how about pitch? It would have been easier to state my opinion if I both clips were identical excerpts.

                          Did I answer your question?

                          ST

                          Comment


                          • Clip 1 v 6

                            No I don't think you did answer his question but went at a tangent.

                            Are you saying that you cannot tell any difference between the quality of Clip 1 and Clip 6 in Alan's last post? (ignore level differences). I don't think judging sound quality has any relationship to your exposure to western music or not. The musical genre is not relevant at all. And Alan does not play tricks; this is a serious matter and he is investing his free time into this explanation. I spoke to Alan. Please do not take literally 'awwww'. He's just trying to get over the idea that there is some sort of pitch or tone or even tones in the reverberation of Clip 6. He said use your mouth to sing with the pitch. But you could use the piano or just hear this pitch in your mind as I do. Do you grasp this essential point? Can you hear the difference in the quality of the reverberation between Clip 1 and 6 which both have reverberation, but of different quality. Can you hear that the decay of Clip 1 is even, no pitch in the decay, but in Clip 6 there are some nasty pitch-related effects in the reverberation although the musical notes are the same?

                            Don't hunt for a deeper explanation than is needed at this point.

                            Comment


                            • Clip 1 is better than Clip 6

                              Originally posted by HUG-1 View Post
                              No I don't think you did answer his question but went at a tangent.

                              Are you saying that you cannot tell any difference between the quality of Clip 1 and Clip 6 in Alan's last post?.... Can you hear that the decay of Clip 1 is even, no pitch in the decay, but in Clip 6 there are some nasty pitch-related effects in the reverberation although the musical notes are the same?

                              Don't hunt for a deeper explanation than is needed at this point.
                              I said
                              I have made up my mind the first time I heard the sound that the first recording sounded right. Did I hear the "awwwwww"? Well... I heard musical notes hangover

                              The first recording that I am referring to in my previous post was Clip 1. The noise and notes hangover that I was describing was about clip 6. Clip 1 sounded correct to all of us. I sense clip 6 to be slightly with more reverberation than clip 1 though Alan said clip 6 got different quality and not quantity of reverberation.

                              I repeat, Clip 1 is better than Clip 6.

                              ST

                              Comment


                              • Boosted reverberation quality demonstration ...

                                So you can hear a difference between Clip1 and Clip 6. That's a crucial step.

                                Ignore the exact loudness or even the quantity of reverberation (I made no effort at all to equalise the loudness of 1 and 6, in fact I boosted the loudness of Clip 6). Let's not try and deconstruct the reverberation from the direct sound. That may be a step too far at this stage if you are not familiar with how large spaces (halls, churches etc.) sound when you are in them. Let's just concentrate on the overall sound, whether or not it is the contribution of the direct (instrument only) sound or the sound of the acoustic space around the instruments (reverberation etc.) or some combination of the two which is actually what we are hearing. Let's just grade the overall sound regardless.

                                BTW, I am not much interested in opinions about the quality of any clip or listener preference for one over another. We're gathering facts and it's far too early to start making preference decisions. We only need to hear differences if we can. OK, let's stop playing around and make the quality of the reverberation a more prominent feature of the clip. Yes, there is a lot of reverb (a large quantity) but that's not important. I hope that you can now clearly hear that there is a dominant quality issue with the reverb. It has a pitch to it. It has tonality. It is ever-present throughout. And its horrid sonic character is fed by the music.

                                [Clip #7] (Dominant reverberation character)

                                But how has that happened? Are the musicians playing the same notes at the same loudness. Absolutely yes. Have additional musicians been drafted into the recording playing some weird instruments that have a drone in a narrow band of frequencies - some sort of bagpipes perhaps? Definitely not. All that's different is that I've just added a special sort of synthetic reverberation to the original dry clip. Has the PA system gone mad? There was no PA system, but in fact, this is not such a stupid suggestion as it may seem. Why?

                                ====================

                                After listening to that Clip 7 a few times my ears are ringing .... so here to reset yours is what an even, sweet, characterless acoustic space around instruments and voices should sound like - recorded in a church in 1961:

                                [Clip #8]
                                Alan A. Shaw
                                Designer, owner
                                Harbeth Audio UK

                                Comment

                                Working...
                                X