On 2014-09-11, Jim Lesurf wrote:
In article , William Unruh
wrote:
On 2014-09-10, Jim Lesurf wrote:
In article , William Unruh


So use sox say to impliment the inverse RIAA, then use audacity to
look for those spikes, and remove them, then use the RIAA on the
result. Note that one could just take the derivative, but that would
still leave a finite spreading due to the treble/bass boost.

Wary of that because 'mending' a differential waveform might lead to a
dc offset problem when you re-integrate the result. So I'd use a dx/dt
or

You could always put in a 50 or 30 Hz cutoff in the RIAA curve. Some
advocated that anyway. But those clicks put in a DC bias in the first
place.

Erm. The mechanics and the RIAA don't pass down to dc. So what happens is a
decaying offset. The results shapes are pretty clear. In my case I'm using
a V15 in an old arm that has more mass than ideal. So the peak and fall at
LF is at very low frequency, but not dc.

Actually, the RIAA curve does go to DC. There was a very controvertial
proposal to put another zero/pole at 50Hz to comensate for the cutter
low freq resonance but the problem is that the cutters all have
different resonances to for some it would make thing worse.
Anyway, since your speakers cannot hear 30Hz, you could put it there--
the main thing is that the unRIAa and RIAA filter be complementary.

If the spike from the record is before the RIAA then the RIAA filter
will have spread it out all over the place, and "fixing" it after the
filter will leave all that spread out residual in place.



d2x/d2t to *find* and list click locations. But do any editing on the
actual audio file recorded using RIAA. Avoids the problems of dealing
with the real response curve being rather complicated.

But since the click has been spread out all over hells half acre by
RIAA, that "fixing" either leaves loads of artifacts or also "fixes" a
bunch of the real signal as well.

The pre RIAA is the place to fix it.

Again, looking at the shapes I can see the effects. Adding the 'fix' just
puts in a plausible smooth interpolation anyway.

To deal with it in the way you suggest would require an accurate 'de-riaa'
that also precisely deals with the stylus and arm responses over the full
range down to almost dc. i.e. much lower than 10Hz or so. Even measuring
that isn't trivial. And it differs in the vertical and horizontal planes
anyway. So you'd also have to convert the L and R to V and H first.

So simply applying a reverse riaa preamp curve won't in practice be much
better than a simple integrator if your concern is LF spread.

Agreed that the curve is problematic below 50Hz. But even at 200Hz the
sound is spread out over more than 200 time pixels (400 for 96K
sampling). That's a lot.



Given that the mends I've made so far are generally inaudible except for
severe events that clearly lose the waveform anyway. I'm happy enough
despite the nice theory for preferring de-riaa. Life's too short. :-)

It is cheap enough to try it. I agree that it may not be an improvement.
Even just a differentiator would be a
help (differentiate, fix, integrate) except you really have to make sure
you have enough dynamic range. Since that is 10 octaves or 60dB emphasis
of highs over lows, which is even larger than the 48dB of the RIAA
curve ( which would fit in another 8 bits that sox stores stuff at.)



Jim