Music at -60 db

Lazarus Short

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#1
I got a CD in the mail yesterday from ebay - Tapani Varis, NSD 6011. I just have this goal to collect NorthSide Digital's entire catalog, and have 30 CD's to go. This particular CD is not likely to ever become a favorite, as it is Jew's harp music, but I did find this out: my preamp has a readout which goes down to -61 db. On starting this disc, at -60 db, there was music - not loud, but I could hear it. Most discs don't show up to the ear until about -50 to -40 db. Remarkable...
 

Lazarus Short

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#3
OK, when I run the volume up on most CD's, it usually takes some cranking to hear the music...that is, if I remembered to turn the power amp on.

On this particular CD, I got music that I could hear just going from -61 db to -60 db.

Are you on your third cup now?
 
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#4
Interesting, I have never paid attention to what you have noticed but it does seem strange. I thought that one’s and zeros weren’t affected by gain in the recording process like analog? Perhaps the disk material itself or the depth to which it was burned?
 

Lazarus Short

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#5
Interesting, I have never paid attention to what you have noticed but it does seem strange. I thought that one’s and zeros weren’t affected by gain in the recording process like analog? Perhaps the disk material itself or the depth to which it was burned?
I don't know if the volume is encoded in the ones and zeroes or not - anybody know?
 

Gepetto

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#6
Interesting, I have never paid attention to what you have noticed but it does seem strange. I thought that one’s and zeros weren’t affected by gain in the recording process like analog? Perhaps the disk material itself or the depth to which it was burned?

??
 

J!m

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#10
Ok! Both synapses firing now...

Yes, there are a couple things at work (typically) with CDs

1) compress the $#!+ out of it, and run at -1dB (or -0.5 in a few rare cases) peak.
2) Use of "Deemphasis" bit on the CD

The latter has an encode when recorded that is (or should be) decoded on playback. Not used much any longer but on old first-gen CDs it was used a lot. A nice feature of my old D2A is to detect, and deemphasize those with this bit on. Big difference playing on other players that do not recognize, or perhaps simply ignore, the deemphasis bit.
 

J!m

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#12
The emphasis option can be thought of as an RIAA eq thing.

Or Dolby NR.

If it’s encoded with it, it should be decoded for playback.

I think the intent was to assist the high frequency brick wall filter to not sound like poop. But that’s just my immediate theory. It really isn’t used any longer, but old CDs with it may sound over-bright and a bit louder with DACs (internal or stand alone) that ignore the bit.
 
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#14
Yup, now that I reread that, I am not sure what I was trying to say. I think maybe I was remembering something I read about the difference between the way commercial CD’s are encoded and the way CDR/CDRW’s are encoded.
Regardless it obviously made no sense in this discussion.
Disregard and carry on.
 

J!m

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#15
For digital audio (unlike just about everythig else) there is a hard and fast rule for the definition of "0dBFS"

dBFS
When digital audio emerged, it needed its own dB system, which brought the need to choose a reference. But there was a problem:

Digital audio can be 8 bits (sample values from 0 to 255) or 16 bit (0..65535) or 24 bit (0..16777216).

It seems like the common thing in all these bit depths is the zero, but we can't use it as a reference as we'll get:

dBFS = 20log(m / 0)​
While this is sufficient to rule out 0 as a reference, there is another fact to consider: We know that during ADC a higher bit depth extends the dynamic range downwards not upwards. In other words, the loudest analog voltage an ADC supports always translates to the highest value the bits can represent. If the analog limit is 1V, in an 8 bit system it will get a sample value of 255, but in a 16 bit system it will get 65535.

This make the choice rather obvious - the reference for dBFS should be the highest sample value of the system bit depth. So:

dBFS = 20log(sample value / highest possible sample value)​
Now in logs, if the numerator is smaller that the denominator, you always get a negative result; if the two are equal, you get 0. So in the case of 16 bits:

0dB = 20log(65535 / 65535)​
and

-6dB = 20log(32768 / 65535).​
Since the sample value can never exceed the highest sample value, dBFS values are always equal to, or smaller than 0.

From this article/blog/forum whatever. Lots of fun reading...
gain - What is 0 dB in digital audio? - Sound Design Stack Exchange
 

marcok

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#17
However in our hobby ,
we generally use relative levels and not absolute levels .
For example we use dB to define gain and loss :
this line amp has a 15 dB gain or this phono amp has a 45 dB gain @ 1khz
In these case dB is only a number and not a value !
Anyway ,for me , it's correct to know what there's about this matter .
Ciao
Marco
 

J!m

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#19
That link I put above gets onto the history of the Bell, and all the different flavors.

With analogue recording and playback, there’s leeway. But, we discovered my Tascam cassette deck (for example) has a “0dB” that is about 3dB over most other consumer cassette decks.

Digital has the brick wall and you can’t cross the line! So they had to determine a true standard.
 
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