Failure of Soundcards to Deliver Full Scale Samples
Some time back a user reported to me that when recording via his Ensoniq
AudioPCI soundcard, it is impossible to set it up to deliver full-scale
samples. I acquired a Creative AudioPCI card (which uses the Ensoniq 1373
sound chip) and reproduced the problem. It would appear that the analogue side
of the card has an input saturation or clipping problem, and I have been
unable to find a solution.
From postings I have seen on the Internet, it seems that this problem is
common to many cards based on the Ensoniq 137x series of sound chips.
Although the loss of dynamic range (about 2dB)
is largely academic, it does make metering very difficult. In particular,
Wave Repair can never detect clipping because it happens in the analogue
domain before the signal is digitized by the card.
Therefore if you suspect your soundcard might have this problem
I suggest the following experiment:
- Try recording something with Wave Repair with the input level turned right up.
Note whether the red "clip" LED on Wave Repair's level meters comes on.
- If no clipping is reported, then it is likely that your card has this problem.
You can verify this by zooming in on loud sections and looking for waveforms with
the tops chopped off and replaced by a ragged flat line.
In this case, it would be best to set record levels to peak no higher than about
-4dB in order to avoid any possibility of clipping.
- If you do see clipping reported,
then your card does not suffer from this problem and you can safely use the full
dynamic range when recording.