In article ,
Richard Crowley wrote:
It operates under Debian Linux, but I also tested it under Windows XP,
with same results. The input volume for digitilizing vinyl records is
too low, and I can't enhance it.
You must use an RIAA phono preamp between the pickup cartridge and the
line input to the sound card. AFAIK, there are NO computer audio cards
which have inputs appropriate for phono cartrdges (47K input impedance,
high gain, and the RIAA equalization curve).
Yes, I do have a RIAA phono preamp between the two.
Then either the phono preamp output is too low or the 2496
card input gain is too low. The common differential diagnosis
techniques would quickly identify which was the case.
One possibility, I suppose, is that the OP is using a low-output
moving-coil cartridge. These require some form of additional
step-up device (either a transformer, or a "head amp") prior to the
normal RIAA preamplifier.
It might also just be a relatively low-level moving-iron or
moving-magnet cartridge.
Another possibility is that the RIAA preamp was designed for the older
consumer standard ("full output" being 1 volt peak-to-peak) but that
the Audiophine 2496 is designed for the newer (CD-era) consumer
standard ("full scale input" being 2 volts peak-to-peak). This would
result in a 50% reduction in apparent input level.
An additional question for the OP: just how much "too low" is the
signal level once you've digitized it?
If the highest peak volume level you're seeing on your LPs is, say,
up to 25% of full-scale, then I'd actually recommend that you not
fiddle at all with the input gain. If you need to normalize, do so in
the digital domain after capturing.
Here's why.
There can be a fairly wide variation in the peak signal level of LPs.
Different manufacturers "cut" the albums differently. There's a
complex tradeoff between maximum cutting level, play time per side,
background noise level, and distortion. I've had some particularly
aggressive albums whose peak levels seemed to be almost 10 dB above
that of albums with a quieter cutting (although this is a fairly
extreme case).
In my opinion, when digitizing LPs, the most important thing to do is
make sure that the highest peak level, on the "hottest" LP, doesn't
clip. Clipping sounds really nasty, and cannot be corrected properly.
The dynamic range of even a 16-bit audio capture is significantly
greater than the dynamic range of an LP... even that of a
mint-condition, never-before-played LP pressed on really good virgin
vinyl. You can afford to throw away a couple of bits of dynamic range
at the top end, by having your average input level down at half- or
quarter-scale, in order to avoid the risk of clippping; the quietest
passages on the LP, and the residual surface noise will still be
comfortably far above the 16-bit quantization threshold.
This is even more true if you have a "24-bit" converter, and can
capture audio in a 24-bit format. I say "24-bit" because such
converters usually don't have a true 24-bit dynamic range... last time
I looked the better ones were in the 21- to 22-bit range.
Nevertheless, there's plenty of range here - quite a bit more than an
LP requires.
Best recipe: capture in a 24-bit format (with the input gain adjusted
to keep the worst-case peak on a really loud record some distance
below full-scale), edit (clean up pops and ticks), then convert to
16-bit format (gain-boosting to normalize while still avoiding
clipping, if you wish) using a decent dithering algorithm.
--
Dave Platt AE6EO
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