cliveb Wrote: > 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 Clive,
Since I'm not a recording engineer, and I don't know a least significant bit from a hole in the ground, please confirm that that my simple English description conforms to what you have said: 1. Record LP with peaks no higher than -12db. (The meters in Sound Forge hold their highest value, so this should be easy to do with a couple of passes.) 2. Normalize Correct? I'm going into a Audiophile 2496, too. -- jonheal Jon Heal says: Have a nice day! http://www.theheals.org/ ------------------------------------------------------------------------ jonheal's Profile: http://forums.slimdevices.com/member.php?userid=2133 View this thread: http://forums.slimdevices.com/showthread.php?t=21836 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
