Re[2]: 16-Bit Stereo PCM Standard?
Peter Mulholland <[email protected]>
| Newsgroups | gmane.comp.lib.openal |
|---|---|
| Message-ID | <[email protected]> |
Hello Patrick, Tuesday, April 6, 2010, 1:33:35 AM, you wrote: > Though it may be true that the actual loudness isn't of OpenAL's > concern, I still think it would be the case that the _relative_ > loudness of two given PCM samples is of OpenAL's concern. > How relative loudness works still confuses me. There has be something > very well defined about what the difference between the PCM values > 1,332 and 3,318 should be, in terms of decibels produced. Or else I'm > just lost. > Let me know if I'm barking up the wrong tree, but I really don't think I am :-) What you might see described for digital audio is dBFS. This is basically sound output level relative to the DAC's maximum output. The best way to think of it, is that the sample data describes a percentage of the DAC's maximum output. 32768 would mean 100% positive voltage, and -32767 would mean 100% negative. Sometimes you see floating point format used, and this is scaled from -1.0 to +1.0 >From a handy website: dBFS - dB Full Scale 0 dBFS represents the highest possible level in digital gear. All other measurements expressed in terms of dBFS will always be less than 0 dB (negative numbers). 0 dBFS indicates the digital number with all digits ="1", the highest possible sample. The lowest possible sample is (for instance for 16 bit audio): 0000 0000 0000 0001, which equals -96 dBFS. Therefore the dynamic range for 16-bit systems is 96 dB. For 20-bit digital audio it is 120 dB. For 24 bit digital audio it is 144 dB. Full-scale input level is the analog input voltage level that will cause the A/D converter to just equal full scale with no clipping on either positive or negative peaks. Output full scale is defined as the analog output voltage produced while playing a 997 Hz digital full-scale sine wave, assuming the THD+N is less than -40 dB relative to the signal level. -- Best regards, Peter mailto:[email protected] _______________________________________________ Openal mailing list [email protected] http://opensource.creative.com/mailman/listinfo/openal