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Topic: AES 2009 Audio Myths Workshop (Read 170116 times) previous topic - next topic
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AES 2009 Audio Myths Workshop

Reply #400 –
Quote from: John Eppstein on
3 frequencies aren't enough for rigorous testing,


I agree that 3 frequencies aren't enough if you are starting with a blank sheet of paper.

Thing is, we've been testing audio gear pretty intensively for many decades -  5 more or less.  The sheet of paper isn't blank for many kinds of audio gear. It is very rare to find say a power amplifier whose frequency response can't be accurately characterized with just 3 measruements.  Ditto for nonlinear distortion. If you are a little paranoid - run a sweep or a multitone. No biggie!  At PCAVTech I ran a multitone, and RMAA runs a sweep.

AES 2009 Audio Myths Workshop

Reply #401 –
Quote from: Woodinville on
Each DOUBLING of inputs added AT THE SAME LEVEL adds 3dB to the noise level

Yes, though few multi-track mixes have all tracks playing at full volume. Much more typical is to record each instrument at full volume for best s/n. Then when mixing, later many of those tracks will be lowered. When I used to mix full time professionally in the 1970s and 80s, often the bass and kick drum were the loudest instruments! A little treble roll-off on playback would reduce the tape hiss nicely. Then many of the other instruments would be mixed in at a lower level, so it's not like 16 or 24 tracks are all adding noise at full scale.

--Ethan
I believe in Truth, Justice, and the Scientific Method

AES 2009 Audio Myths Workshop

Reply #402 –
Quote from: Woodinville on
Noise growth.

Each DOUBLING of inputs added AT THE SAME LEVEL adds 3dB to the noise level, for decorrelated (i.e. thermal, or the like) noise.

2 inputs -3dB to SNR
4 inputs -6
8 intputs -9
16 inputs -12

This is true if both INPUTS and NOISE are decorrelated.

Whoa there, that's wrong, chief.

If both input and noise are decorrelated, the overall SNR will not change, although the noise floor and signal floor will both rise.

My comment above is true if and only if you have one signal and 'n' channels of silence.
Quote
However, if we have the same signal in all the mikes, now the signals add in amplitude vs. noise in power.  Then, you get exactly the opposite growth, instead of -3dB you get +3dB, and so on.

This case is true, for example, in things like array mikes. It's not usually a factor in mixing applications.


My coffee must have sunk in before I wrote the second part. It's right.
-----
J. D. (jj) Johnston

AES 2009 Audio Myths Workshop

Reply #403 –


In much the way that the argument "if God had wanted man to fly, he'd have given him wings"...

If God had got the additive quality of recorded noise right, we wouldn't have had to invent GATES.


It is VERY COMMON in multitrack mixing to employ muting and gating on source tracks, due to the objectionable buildup of noise.  (not just skroinks and breath noise, and chair squeaks, either...but noise) 


...remember, Ethan...compressors are in rampant use, and they raise the noise floor!

AES 2009 Audio Myths Workshop

Reply #404 –
Quote from: dwoz on
In much the way that the argument "if God had wanted man to fly, he'd have given him wings"...

If God had got the additive quality of recorded noise right, we wouldn't have had to invent GATES.


I don't think that anybody is seriously disputing that.

The quesiton is: "Where does the noise come from?"

The answer for equipment of even modest quality is: "The room the recording is made in".

Quote
It is VERY COMMON in multitrack mixing to employ muting and gating on source tracks, due to the objectionable buildup of noise.  (not just skroinks and breath noise, and chair squeaks, either...but noise)


So Dwoz you're saying that in all of your years of studio experience, you have never noticed that the most common source of background noise in your recordings was the room?

<Mental image of Dwoz spending the big bucks for a Millenia Multimedia Mic Preamp and an Apogee Rosetta ADC to reduce background noise!>

AES 2009 Audio Myths Workshop

Reply #405 –
Quote from: Arnold B. Krueger on
The answer for equipment of even modest quality is: "The room the recording is made in".


I think it is important to talk about the frequency ranges when we talk about noise. Room noise, in my experience, is predominantly a mid-low frequency phenomenon, whereas electronic noise, tends to be 'white', and is most problematic at high frequencies. So a high level of room noise may not mask electronic hiss.

AES 2009 Audio Myths Workshop

Reply #406 –
Quote from: Iain on
Quote from: Arnold B. Krueger on
The answer for equipment of even modest quality is: "The room the recording is made in".


I think it is important to talk about the frequency ranges when we talk about noise. Room noise, in my experience, is predominantly a mid-low frequency phenomenon, whereas electronic noise, tends to be 'white', and is most problematic at high frequencies. So a high level of room noise may not mask electronic hiss.


Actually, the ear is most sensitive around 4 KHz, which is pretty close to midrange, and therefore neither a high or low frequency.  The spectral content of electronic noise is difficult to generalize on, because it has different shapes depending on types of components and even specific examples.  In short, your generalities are highly hedged and not generally relevant to any particular situation. If HVAC noise due to turbulent air flow is audible, it often is actually pretty hissy. 

If you are actually doing real world recording, about the only time you hear electronic noise from the mic preamp is when the mic is disconnected or in the case of a condensor mic, the phantom power is turned off. Simply disconnecting a mic is not a reliable indicator of the mic preamp's noise because the input termination is a strong determining factor. Make the mic operational, and in almost every circumstance, "room tone" noise will dominate. The rest of the recording system will generally be free of audible noise unless you turn some gain control way up.

One of the mics I use quite frequently is the Rode NT4 which is alleged to be one of the quietest mics around. Since it is a condensor mic, its output is quite high, and as usual, room tone dominates its background noise in actual use.

AES 2009 Audio Myths Workshop

Reply #407 –
Indeed, unless you are a perceptual coding expert, it is dangerous to assume that a louder sound will mask a quieter one. The original question here is whether performance of modern digital audio electronics can be a limiting factor in recording quality. Because in some recordings, room noise is considered to be part of the program material, and because analog electronics with >100 dB S/N exist, the answer to that question has to be "yes".

AES 2009 Audio Myths Workshop

Reply #408 –
Quote from: Notat on
Indeed, unless you are a perceptual coding expert, it is dangerous to assume that a louder sound will mask a quieter one. The original question here is whether performance of modern digital audio electronics can be a limiting factor in recording quality. Because in some recordings, room noise is considered to be part of the program material,


Looks to me like a claim that in every case room noise is 90 or more dB down, and/or has a spectral balance that is violently different from that of electronics.  Just 'taint so!

Quote
and because analog electronics with >100 dB S/N exist, the answer to that question has to be "yes".


Hmm, so common 24 bit digital interfaces with => 110 dB SNR have been excluded from the discussion?

Seems strange, given that even an alleged bottom feeder like me has several of them.

I'm sticking to my story - even with legacy 16 bit converters, I'm getting very clean recordings of the room tone.

Feel free to post your own recordings of exceptions.

AES 2009 Audio Myths Workshop

Reply #409 –
Quote from: Notat on
Because in some recordings, room noise is considered to be part of the program material, and because analog electronics with >100 dB S/N exist, the answer to that question has to be "yes".


That is an important point. Room 'noise' may be signal and therefore should not be factored into the debate. For example, if I am recording some office ambience for a TV show/movie, the room's 'noise' is the signal.

I'm not making the call that modern audio electronics are/are not good enough, just saying that you can't use room noise an easy out.

AES 2009 Audio Myths Workshop

Reply #410 –
Quote from: Iain on
Quote from: Notat on
Because in some recordings, room noise is considered to be part of the program material, and because analog electronics with >100 dB S/N exist, the answer to that question has to be "yes".


That is an important point. Room 'noise' may be signal and therefore should not be factored into the debate. For example, if I am recording some office ambience for a TV show/movie, the room's 'noise' is the signal.

I'm not making the call that modern audio electronics are/are not good enough, just saying that you can't use room noise an easy out.


There is typically  25-30 dB between room noise and the electronics, and that is true even when you restrict yourself to just 16 bit electronics.

Room noise isn't an out, it is a brick wall that is right there in your face.

This isn't just theory. I got very interested in this last year and took a PC with a  ca. 110 dB SNR/DR 24 bit card on site a number of times. I had several opportunities to take data in very quiet rooms.

AES 2009 Audio Myths Workshop

Reply #411 –
Quote from: Arnold B. Krueger on
Quote from: Iain on
Quote from: Notat on
Because in some recordings, room noise is considered to be part of the program material, and because analog electronics with >100 dB S/N exist, the answer to that question has to be "yes".


That is an important point. Room 'noise' may be signal and therefore should not be factored into the debate. For example, if I am recording some office ambience for a TV show/movie, the room's 'noise' is the signal.

I'm not making the call that modern audio electronics are/are not good enough, just saying that you can't use room noise an easy out.


There is typically  25-30 dB between room noise and the electronics, and that is true even when you restrict yourself to just 16 bit electronics.

Room noise isn't an out, it is a brick wall that is right there in your face.

This isn't just theory. I got very interested in this last year and took a PC with a  ca. 110 dB SNR/DR 24 bit card on site a number of times. I had several opportunities to take data in very quiet rooms.



20 dB(A) as noise level is not uncommon in recording rooms. Now when you use 24 bits format, it's more about security and headroom. You can peak at -10 to stay on the safe side, and that is the main reason this word lenght makes sense for recording music.

Now on the delivery side, the most dynamic orchestra should be what ... Around 60 dB, so yes, 16bits makes sense.

Few professionals are arguing that 16bits is not adequate as delivery format. So far, the 24bits/96kHz attempts when down to the toilets.

malice

AES 2009 Audio Myths Workshop

Reply #412 –
Quote from: malice on
Few professionals are arguing that 16bits is not adequate as delivery format. So far, the 24bits/96kHz attempts when down to the toilets.
There have been successful ABXes of mixed/mastered 16-bit vs. 24-bit on these very forums on moderately dynamic orchestral content. While I'd tend to agree with you that 16-bit audio is adequate for delivery, it is not sonically transparent for all listeners in some cases.

AES 2009 Audio Myths Workshop

Reply #413 –
And by the way, the noise floor in analog is just not the same as in digital.

The tape hiss is far more acceptable to our ears than quantification noise.

That explain as well the need of staying on the safe side. 16bits is the minimum workable format in digital. Analog doesn't need dolby SR to be workable.

malice

AES 2009 Audio Myths Workshop

Reply #414 –
Quote from: Canar on
Quote from: malice on
Few professionals are arguing that 16bits is not adequate as delivery format. So far, the 24bits/96kHz attempts when down to the toilets.
There have been successful ABXes of mixed/mastered 16-bit vs. 24-bit on these very forums on moderately dynamic orchestral content. While I'd tend to agree with you that 16-bit audio is adequate for delivery, it is not sonically transparent for all listeners in some cases.


I agree with this but:

1) I wouldn't change my classical CD collection for that reason only, so the reason it was not a success was commercial. Not good enough to justify the expense

2) Pop/Rock/dance/rap etc : 16bit migh sometimes be already to much. (big tongue in cheek comment here )


malice

AES 2009 Audio Myths Workshop

Reply #415 –
Quote from: malice on
And by the way, the noise floor in analog is just not the same as in digital.

The tape hiss is far more acceptable to our ears than quantification noise.


Wrong again!

The fact of the matter is that tape hiss is defined by classic and well-understood physical processes. Besides being about 40 dB worse than the best of modern digital (!!!!), it also is simply what it is, and there is very little that hasn't already been done about it yet to be done. We can't massage tape hiss so that its spectral contents fall where the ear is least sensitive. Everybody with a brain gave up developing analog tape technology about 30 years ago because it was a technological black hole, just like vinyl.

In contrast, so-called noise shaping of quantization (note the use of the proper word) errors can be pretty much whatever we want it to be.

First off, digital quantization noise can be as small as we want it to be. The current limits to the noise floor of ADCs is set in the analog domain. The last time there was a significant improvement in ADC performance a whole new generation of op amps had to be developed so that the new ADCs could even be measured.

Secondly, spectral shaping of quantization noise is itself a very mature technology that just works. While some may dispute claims that spectral shaping of quantification noise of a 16 bit system can be made the perceptual equivalent of 120 dB SNR. tremendous improvements are possible. In fact there isn't a lot of worry about spectral shaping of the quantization noise of the best ADC chips because their noise is so rediculously low compared to the environment that they work in.

When you're comparing tape hiss to the noise floors of the best digital systems, it is a comparison between the tape hiss you hear, and effectively silence. Letsee we set the listening level to say 100 dB, and the digital noise is 20 dB below the threshold of hearing in the quietest room on earth. There isn't even a comparison!

AES 2009 Audio Myths Workshop

Reply #416 –
Quote from: Arnold B. Krueger on
Quote from: malice on
And by the way, the noise floor in analog is just not the same as in digital.

The tape hiss is far more acceptable to our ears than quantification noise.
Wrong again!
Not just wrong, in violation of Term of Service 8. You're making (disputed) claims about audio quality without any kind of scientific evidence.

AES 2009 Audio Myths Workshop

Reply #417 –
Quote from: Canar on
There have been successful ABXes of mixed/mastered 16-bit vs. 24-bit on these very forums on moderately dynamic orchestral content. While I'd tend to agree with you that 16-bit audio is adequate for delivery, it is not sonically transparent for all listeners in some cases.


Do you have a link? I find this somewhat questionable. Except when you turn up the volume so high, that it would damage your ears during full scale passages.

AES 2009 Audio Myths Workshop

Reply #418 –
Quote from: googlebot on
Do you have a link? I find this somewhat questionable. Except when you turn up the volume so high, that it would damage your ears during full scale passages.
http://www.hydrogenaudio.org/forums/index....st&p=610558

I was quite skeptical at first as well. My friend (and fellow member) Case succeeded as well, and I trust him, so I accept their claims. The thread is long, but we get it sorted out in the end.

AES 2009 Audio Myths Workshop

Reply #419 –
Quote from: Canar on
Quote from: Arnold B. Krueger on
Quote from: malice on
And by the way, the noise floor in analog is just not the same as in digital.

The tape hiss is far more acceptable to our ears than quantification noise.
Wrong again!
Not just wrong, in violation of Term of Service 8. You're making (disputed) claims about audio quality without any kind of scientific evidence.


Ok, fair enough.

May I rephrase this :

Would any of you make a record with 10bits converters ?

We can make a test if you want, let's reduce the word lenght of 16bits tracks to 10 bits and let's see if it's workable ?

malice

AES 2009 Audio Myths Workshop

Reply #420 –
Quote from: Canar on
Quote from: googlebot on
Do you have a link? I find this somewhat questionable. Except when you turn up the volume so high, that it would damage your ears during full scale passages.
http://www.hydrogenaudio.org/forums/index....st&p=610558

I was quite skeptical at first as well. My friend (and fellow member) Case succeeded as well, and I trust him, so I accept their claims. The thread is long, but we get it sorted out in the end.


The 24/96 sample (96k24b.wav) has a maximum peak amplitude that is about 20 dB (more than 3 bits) below FS.  This shifts the comparison from a purported comparison of 16 bits versus 24 bits to an actual comparison of a little less than 13 bits to almost 21 bits.  This example totally fails the criteria of demonstrating good gain staging.

The sustained low level passage in 24.wav peaks at around 40 dB below FS...

Where things get strange is when the auditions are not done using equipment that is really clean below the 16 bit level.  I've always done my work with equipment that had SNR and DR of > 100 dB right up to my ears. Right now my daily driver for routine tests has almost 110 dB DR and SNR,

AES 2009 Audio Myths Workshop

Reply #421 –
Quote from: Canar on
I was quite skeptical at first as well. My friend (and fellow member) Case succeeded as well, and I trust him, so I accept their claims. The thread is long, but we get it sorted out in the end.


While I believe that your trust is justified, I wouldn't exactly call a 5.9% score quotable. For such a hotly debated issue, with all the inflow "high rez" bullshit, that Hydrogenaudio has to fight off each year, I think it is not to much to ask to provide a ~0% result. Especially if we have the situation of a respected member being sure, that he can hear a difference. As another member put it: Why not "go the extra mile"?
 

AES 2009 Audio Myths Workshop

Reply #422 –
Quote from: Canar on
Quote from: googlebot on
Do you have a link? I find this somewhat questionable. Except when you turn up the volume so high, that it would damage your ears during full scale passages.
http://www.hydrogenaudio.org/forums/index....st&p=610558

I was quite skeptical at first as well. My friend (and fellow member) Case succeeded as well, and I trust him, so I accept their claims. The thread is long, but we get it sorted out in the end.
After hanging in there for a long time (it's a very interesting thread!), I missed the end. It seems Case ABXed the file provided by KikeG - that wasn't standard noise shaped dither. He was the only person to report any result (positive or negative) from that file. It's probably still valid, but it's not quite the confirmation people were looking for.

We got very close in that thread - but unless someone else can reproduce the results, or Martin can reproduce them on something other than his laptop's built-in sound card, then this isn't much of a result.

Files are here:
http://www.hydrogenaudio.org/forums/index....st&p=626692

Please post any results in that thread, not here.

Cheers,
David.

AES 2009 Audio Myths Workshop

Reply #424 –
Quote from: 2Bdecided on
Files are here:
http://www.hydrogenaudio.org/forums/index....st&p=626692

Please post any results in that thread, not here.


The 24/96 file has such low maximum peak levels that it nets out to be a comparison of less than 13 bits to more than 20 bits.  It's a little bit more relevant than the recent proposal of 10 bits versus 16, but not much.

The 24/48 file has almost 20 seconds of music where the average RMS level is more than 35 dB down.  Given that we have ABX tools that allow the listener to select subsets of test files, this file is too easy to mistakenly slip into a comparison of less than 10 bits to more than 17.  So now we do have a comparison of 10 bits versus 16 (or more)!

Until adequate safeguards are in place in tests involving the second file, we have no relevant test possible with these files on the grounds of a real and present danger of improper gain staging. The first file cannot be helped by controlling listening test procedures. It is effectively moot. The second file could be used with appropriate safeguards that would control which subsets of it were used.