cerberus wrote on Tue, 04 April 2006 10:53 |
Izhaki wrote on Mon, 03 April 2006 22:16 | Maybe I should clarify a few points here:
Cerberus: As mentioned before, 24Bit Integer and 32Bit float has the same effective wordlength: 24 bits. In other words they have the identical digital quality. Hence when having two files of the same quality, it is an advantage if one is 75% in size.
|
if they contain identical data then they are identical quality; otherwise not. a 32 bit float file can contain samples with more information than will fit into a 24 bit file, i would not throw away anything important. jeff dinces
|
Hi Jeff,
The signal out of an AD contains less then 24 good bits. The lower bits carry noise, not audio data.
An acoustic signal (I am not talking about synth) arriving at the AD started with a mic, then a mic pre, and by that time chances are that the noise is much less then 20 bits...
So the best case you can dream off would call for 24 bits carrying music out of the AD.
But then, one goes into the digital world, where it may be important to have a lot more bits for computation of various functions, from digital EQ, to mixing channels and more.
One simple example: you want to add channel A to channel B, but you first want to boost channel A by X2, and attenuate channel B by 2.
Now, the X's are where your bits are, each X can be a 0 or a 1:
Here are the input signals:
Channel A: XXXXXXXXXXXXXXXXXXXXXXXX
Channel B: XXXXXXXXXXXXXXXXXXXXXXXX
Here is A multiplied by 2 (6dB boost) and B divided by 2 (6dB cut):
Channel A: XXXXXXXXXXXXXXXXXXXXXXXX0
Channel B: 0XXXXXXXXXXXXXXXXXXXXXXXX
Each processed channel now has one more bit (25 bits each) and when you add them you have to be ready for at least 25 bits...
So of course for a lot more processing, and with a lot of channels, the digital processing calls for a lot of bits.
But there is no magic. The signal limitation imposed by the mic, micpre, AD and possibly other gear inserted in series already set the limits on what is possible. Adding bits in the digital world allows all sorts of signal "manipulation", but the signal processing operates on a signal with distortions and noise already determined by the previous gear.
Of course, at the end of digital processing, one ends up with "extra bits" that need to be removed, because they contribute nothing and only "take space". Some extra bits may be "on top", some "on the bottom". So we make it into a 16 bit word for CD, or 24 bit format...
Then, once again we are getting out of the digital world into the analog, where we need to have voltage varying with time, not just a bunch of 0's and 1's. That calls for a DA. So once again we are facing real hardware, where we can not even do 24 bits, because the lower bits are buried in noise.
So 24 Bit is more then enough for conversion, and far less then enough for digital processing work. There are "conversion bits" and "digital processing bits" and they are different issues with each one.
And from hearing stand point, 24 bits of sound means 144dB dynamic range which is way above what a human can stand. Recalling the fact that the dB is a logarithmic scale, the difference between say 120dB and 144dB may not sound like much (24dB) but in fact it is a huge difference.
You will not be throwing away anything important...
Regards
Dan Lavry
http://www.lavryengineering.com