Phil Leigh;578558 Wrote: > A -90dB sine wave is just "not there" in normal music. I'd like to hear > JA's justification of why he thinks this is meaningful?
Just saw this question. If you are talking about the undithered tone at -90.31dBFS I show in all my DAC measurements, I use this signal, not because it will be typical of music, but because it is diagnostic for DAC problems. In 2s-complement PCM encoding as used on CD, the change in level from digital "0" to +1 LSB actually involves all bits in the 16-bit word changing value. By contrast, the change from "0" to -1 LSB involves just the LSB changing value. So you can immediately see from the symmetry of the waveform, and how well-defined the 3 voltage levels are, whether or not the DAC is sufficiently monotonic and the analog noisefloor is sufficiently low to allow those data to be correctly decoded. In other words, it's a thumbnail indicator of DAC quality. In general, the test is not as useful in these days of sigma-delta DACs as it was when all we had were multi-bit DACs. However, you still come across pathological designs that fail to reproduce this signal properly - see, for example, fig.8 in the Cary review in the September 2010 issue of Stereophile. John Atkinson Editor, Stereophile -- Stereoeditor ------------------------------------------------------------------------ Stereoeditor's Profile: http://forums.slimdevices.com/member.php?userid=40770 View this thread: http://forums.slimdevices.com/showthread.php?t=82050 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
