For a start can we define digital audio? There are discrete time systems and discrete level systems. Now a CD uses a recovered clock so it may be discrete level but it is still not truly discrete time.
If the CD is copied to a storage medium including the very heavy error correction it is possible to assemble a file that may then be reproduced with a new higher accuracy clock source. To the noise limits this could be a discrete time, discrete level system or completely digital. Of course this assumes the original recording did not have any clocks recovered during production. The other issue is that since the recording clock and the reproducing clock will not have a perfect frequency match there will be some pitch shift. But to be reasonable the clock match should be within .001% and well below human perception limits.
Now the discrete time is actually the easier bit to achieve.
Scott it is a very good bet you understand the issues with making a truly linear step accurate analog to digital converter and the same problem in the reciprocal process.
As an old engineering design rule for adequate communications was to have a channel 10 dB better than the signal. Now as human hearing can range from -6 dBa at some frequencies to 135 dBa that would require 151 dB dynamic range or 25 bits.
Now there are lots of folks advertising 24 bits of audio data, but of course they don't mean true 24 bit accuracy.
Now the other shoe to drop is that timing thing or the inverse, frequency response. As one who could hear dog whistles in my youth, I have always found the absolute statement of human hearing range of 20-20,000 hz. to be incorrect. There certainly is research to show that higher bandwidth audio reproduction may be useful.
So if you want to do an ABX test, perhaps we can get a band to play live in a studio while we listen to the reproduced audio through various conversion sizes and filters. Even then there will still be uncontrolled variables, some of which we may not even recognize.
ES
I don't see the relevance of the Shannon limit for a communications channel to human hearing.
Last time I looked the USGS found the quietest location in the US was 14dB SPL and 135dB is dangerous. It's hard to have a conversation about these things unless they are kept relevant to any actual listening experience.
135dB at the last time you can hear normally, because after your ears will be definitively damaged ?
I thought ~120dB was the pain threshold.
And the average background noise of a very quiet room is situated around 30dB.
That makes 90 dB of dynamic.
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Scott and Eperado thanks for trying to bring some semblance of reality to the discussion.
First off I don't think I want my audio system to produce an spl high enough to recreate the true sound level of a gun shot. I would normally have hearing protection on my ears when around a gun so why would I want to recreate that level for any audio sounds? As Scott and Christophe have pointed out also why do I need a system to be so quite that I would normally have to be in a very good anechoic chamber or in a vacuum to be that quite? Even in the middle of the forest we have background noise louder than some of the lower limits spoken of here. So we really have to define what is truly needed and wanted before we go off the rails here and ask for something unnecessary and impractical.
Christophe,
I can only speak of what is going on here in Los Angeles but I will say that many true recording studios have folded, there are many less than in the past. It isn't that there is less recording work to do but the simple fact that people are recording in their home studios and consumer gear is cheap. One of the studios I knew of had two SSL recording consoles and I heard those were costing in the neighborhood of one million dollars each. That and the extensive microphone collections and sound rooms and such will never be recreated. We have seriously changed the recording landscape at least here in my home town. I know one of my neighbors worked in the same studio for about 20 years and now he can't even find a studio to wok in. It is the untrained who are running most of these home studios and that is part of the simple reason some of the dreck is being put on CD or digital media, musicians as recording engineers is not a great thing, they don't care about some of the things that an audio engineer would consider important, they just don't know the science or standards needed to make the most of the technology.
First off I don't think I want my audio system to produce an spl high enough to recreate the true sound level of a gun shot. I would normally have hearing protection on my ears when around a gun so why would I want to recreate that level for any audio sounds? As Scott and Christophe have pointed out also why do I need a system to be so quite that I would normally have to be in a very good anechoic chamber or in a vacuum to be that quite? Even in the middle of the forest we have background noise louder than some of the lower limits spoken of here. So we really have to define what is truly needed and wanted before we go off the rails here and ask for something unnecessary and impractical.
Christophe,
I can only speak of what is going on here in Los Angeles but I will say that many true recording studios have folded, there are many less than in the past. It isn't that there is less recording work to do but the simple fact that people are recording in their home studios and consumer gear is cheap. One of the studios I knew of had two SSL recording consoles and I heard those were costing in the neighborhood of one million dollars each. That and the extensive microphone collections and sound rooms and such will never be recreated. We have seriously changed the recording landscape at least here in my home town. I know one of my neighbors worked in the same studio for about 20 years and now he can't even find a studio to wok in. It is the untrained who are running most of these home studios and that is part of the simple reason some of the dreck is being put on CD or digital media, musicians as recording engineers is not a great thing, they don't care about some of the things that an audio engineer would consider important, they just don't know the science or standards needed to make the most of the technology.
You can pick what ever safety factor or design limit you would like.
However the 14 dB measured outdoors is the wideband noise limit "A" weighted. As most folks can hear signals 30 db below the noise floor that would be lower than the -6 to -8 dB actual threshold of hearing in the frequency band where the ear is resonant.
Now exposure to sound levels above 80 dBa long term will cause hearing loss. A pistol shot will hit 140+ dB. (Sort of the level required for actual instant hearing damage.) I have measured the sound level for a symphony orchestra in performance on stage at peaks of 135 dBc. Even without any safety margins or headroom that still requires 23 bits and allows for no operator error in gain setting.
The interesting thing about measuring a symphony orchestra is that the musicians will insist a forte is always a forte, but in rehearsal it is 10 dB less in level than during the performance. How you bow a violin to do that is a very interesting issue.
Kindy, You may not want to listen at actual performance levels, but it would be nice to be able to record them.
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Cough, cough.
10 points to the first person who points out the hilariously inapt assumptions.
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The dynamic range capability needed for recording music was considered to be 118dB and for playback (professional app) it is 105dB. I already gave this info. via ref.
0.5% as the midrange thd number during playback is Not acceptable and is audible in analog or digital. This is what people hear as why they like all analog better.
Since 24 bit converters are the norm now, there is nothing to be lost by using them. At least it isn't going to be necessary to add an analog dither voltage to the signal, as was advisable with 16 bit converters! That thermal noise will do the job nicely! Other problems with A/D converters get smaller as the number of bits goes up, so using a 24 bit recording and playback converter is certainly Not a bad thing.
Note also that the professional standard level is much higher than home/consumer market and they can get further from the noise floor or have more usable bits. And have those bits right where we listen mostly. Maybe the HiEnd should adopt the pro standards levels. Its a suggestion for High-End designers to make that shift.
THx-RNMarsh
The dynamic range capability needed for recording music was considered to be 118dB and for playback (professional app) it is 105dB. I already gave this info. via ref.
0.5% as the midrange thd number during playback is Not acceptable and is audible in analog or digital. This is what people hear as why they like all analog better.
Since 24 bit converters are the norm now, there is nothing to be lost by using them. At least it isn't going to be necessary to add an analog dither voltage to the signal, as was advisable with 16 bit converters! That thermal noise will do the job nicely! Other problems with A/D converters get smaller as the number of bits goes up, so using a 24 bit recording and playback converter is certainly Not a bad thing.
Note also that the professional standard level is much higher than home/consumer market and they can get further from the noise floor or have more usable bits. And have those bits right where we listen mostly. Maybe the HiEnd should adopt the pro standards levels. Its a suggestion for High-End designers to make that shift.
THx-RNMarsh
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I agree, but temper that with have headroom for transients like the initial few milliseconds of a piano note being struck etc, and not wanting those events to clip. I think CD is about where it should have been, my point was that 32 bits will never be important except during mixing and filtering whilst mastering a released piece of music
Like I said a few posts ago, that -6dBA limit is below the noise threshold, we are getting thermal dither already added at that level, so we dont need to go lower at that end, and at the top end, going to 135 is a one off event, after that you dont need a system that goes to -6 any more..
Wrinkle,
I think you have just pointed out why people can tell instantly that a piano is recorded and not live, the peak instantaneous transients. Mess that up by clipping the signal and you know instantly it isn't real but just Memorex. Same thing on the speaker side, if you can't produce those fast transients without rounding them off you know your not listening to someone playing a piano in the next room, not hard to tell. But get that all right and then your going to be fooled in the next room. Otherwise it is like someone putting there foot on the mute pedal on the piano, it just sounds flat and muted.
I think you have just pointed out why people can tell instantly that a piano is recorded and not live, the peak instantaneous transients. Mess that up by clipping the signal and you know instantly it isn't real but just Memorex. Same thing on the speaker side, if you can't produce those fast transients without rounding them off you know your not listening to someone playing a piano in the next room, not hard to tell. But get that all right and then your going to be fooled in the next room. Otherwise it is like someone putting there foot on the mute pedal on the piano, it just sounds flat and muted.
Ok. As long as you're talking about the recording/mixing/mastering side of things we're cool.
se
You may agree with SE but if you even look at the data such as the Fletcher Munson curves a low frequency tone at 20 hertz will not mask one at 3,000 hertz even at more than 80 dB. down. Requires more than 100 dB. of masking.
Oh, my God. Don't tell-me the same disaster happened in the city of music than in my country ?
In Paris too, most of the big studios had disappeared. Their big volumes, their acoustic treatment and their collection of mikes and effects as well...
And it is all the more incomprehensible that the recording equipment can cost really cheaper nowadays.
Well, there are few left, but for how long ?
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Esperando,
Don't think for a second that the major record labels don't have a hand in all this of the major studios getting the axe. They will gladly allow their artist to go and record their music in their own home studios, think of the money they save not having to pay the costs needed to support those recording studios that have high overhead. I think these days they could care less about quality as long as they are turning a profit. They did it to themselves by overpricing CD's in the first place and then complaining nobody wanted to pay the price. They blamed it all on illegal downloads, I say bs on that one.
Don't think for a second that the major record labels don't have a hand in all this of the major studios getting the axe. They will gladly allow their artist to go and record their music in their own home studios, think of the money they save not having to pay the costs needed to support those recording studios that have high overhead. I think these days they could care less about quality as long as they are turning a profit. They did it to themselves by overpricing CD's in the first place and then complaining nobody wanted to pay the price. They blamed it all on illegal downloads, I say bs on that one.
Digital caused it, while it made it possible for the many to make something mediocre, it also cost the life of some of the better, while digital may be good, It can also produce some lousy ****.. (Pardon my French) yet still the likes of Bob Ludvig, William Orbit , Rick Rubin and the likes still maintain a High Level and regularly turning out magnificent albums, that still sounds better on vinyl btw.
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