P Floding Wrote: > 60dB translates to 10 or 11 bits. So drop 6 or 5 bits and re-dither to > check the impact on sound quality. Does anyone here know of a program > that can null away a specified number of least significant bits and > re-dither? It would be very interesting to test the result. I don't know of a program off-hand that will crop LSBs and redither, but last night I did some casual tests using an audio editor. I had a recording of a vinyl record in a 16bit 44.1kHz WAV file on disk, and extracted a short section from it to play with. What I did was apply an amplitude reduction (in order to truncate LSBs), then re-normalised it to bring the level back up and thus pull the quantisation noise up to a much higher level. This in effect truncates the LSBs *without re-dithering*, so any effects should be even more audible. The results were:
1. Reduce then increase amplitude by 36dB, effectively truncating the bottom 6 bits. This is the "60dB test". The raised quantisation noise was very clearly audible, and completely unacceptable, which suggests to me that, although the dynamic range of the LP is probably less than 60dB, one cannot afford to be cavalier and chuck away 6 bits of resolution when recording. 2. Reduce then increase amplitude by 24dB, effectively truncating the bottom 4 bits. It was very difficult to detect a significant difference after applying this change. I felt that maybe the noise was changed slightly, but never detected that characteristic "zzzzy-ness" of digital quantisation noise. Perhaps better headphones would have revealed a more obvious difference. 3. Reduce then increase by 18dB, effectively truncating the bottom 3 bits. No audible difference. This was no surprise: the surface noise on a vinyl LP is so high that it effectively "self-dithers" the recording at around the 12-13 bit level. So if you have a decent soundcard with a noise floor below -90dB, it's safe to record at peak levels as low as -12dB then normalise. Bear in mind this was a casual, sighted test. The equipment used was: Linn Sondek LP12/Lingo/Ittok/Karma Naim 42.5K used as phono preamp M-Audio Audiophile 2496 soundcard Home built headphone amp Sennheiser HD535 headphones -- cliveb ------------------------------------------------------------------------ cliveb's Profile: http://forums.slimdevices.com/member.php?userid=348 View this thread: http://forums.slimdevices.com/showthread.php?t=21836 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
