Doom9's Forum - View Single Post - 32-bit float

IanB · 5th August 2011, 02:05

Unless you have some digital synthesiser generated music, the sound recording you have will at beast have come via a microphone (physical transducer), a microphone pre-amplifier (noisy analogue device) and then an Analogue to Digital converter. More probably there will be an assortment of mixing equipment involved as well. Out of all this you get a 24bit PCM data stream. This is a set of integer numbers between -8388608 and 8388607 representing the amplitude of the sound and the analogue noise.

To more easily process this data it is converted, losslessly to 32 bit IEEE floating point numbers Unless the processing algorithms cause the numbers to exceed the maximum or minimum permissible floating point value the original sound data will be intact although modified as required by the processing algorithms.

Now when it comes time to play the sound back the 32 bit IEEE floating point numbers need to be converted back to a 24bit PCM data stream. Okay the floating point number can have a values of 123456.789. Do you convert it to 123456 or 123457 ultimately it does not really matter the difference between the 2 values is less than -138db of full scale. And the best analogue amplifiers might approach 100db noise floor. The crap in domestic PC sound cards is often lucky to achieve 50db.

So do you really care about a -138db difference.

5th August 2011, 02:05	#8 \| Link
IanB Avisynth Developer Join Date: Jan 2003 Location: Melbourne, Australia Posts: 3,167	Unless you have some digital synthesiser generated music, the sound recording you have will at beast have come via a microphone (physical transducer), a microphone pre-amplifier (noisy analogue device) and then an Analogue to Digital converter. More probably there will be an assortment of mixing equipment involved as well. Out of all this you get a 24bit PCM data stream. This is a set of integer numbers between -8388608 and 8388607 representing the amplitude of the sound and the analogue noise. To more easily process this data it is converted, losslessly to 32 bit IEEE floating point numbers Unless the processing algorithms cause the numbers to exceed the maximum or minimum permissible floating point value the original sound data will be intact although modified as required by the processing algorithms. Now when it comes time to play the sound back the 32 bit IEEE floating point numbers need to be converted back to a 24bit PCM data stream. Okay the floating point number can have a values of 123456.789. Do you convert it to 123456 or 123457 ultimately it does not really matter the difference between the 2 values is less than -138db of full scale. And the best analogue amplifiers might approach 100db noise floor. The crap in domestic PC sound cards is often lucky to achieve 50db. So do you really care about a -138db difference.