21 Apr
2010
21 Apr
'10
5:17 p.m.
Hello Fons. Almost all consumer portable devices seem
to distort signals
above 16Khz in uncompressed 44100Hz audio. I always wondered about this,
maybe they all have very crappy DA converters, or maybe it is because
the reasons explained by Niels and Arnold in their emails...
It is not the DACs, it is almost always the analog amplifiers. Have a
look at the various noise and distortion measures of audio opamps, the
figures tend to dogleg upward between 10 and 20kHz. It's a
consequence of optimizing for very very deep signal depth below those
frequencies (and to a lesser extent, cost). Even the most expensive
boutique audio opamps show this dogleg, and very few manage to push it
higher than 20-25kHz or so. To do so, you have to sacrifice noise
performance.
You can get opamps that are dead flat with unmeasurable distortion to
100kHz or 1MHz... but you're only going to have 8 bits or less of
signal depth due to voltage and current noise.
Monty