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MMD > Archives > June 2001 > 2001.06.05 > 10Prev  Next

Removing Noise From Old Phono Disc Recordings
By Bill Finch

Removing in real time:

1.  SAE made a "click, pop, scratch eliminator" 20 years ago.  It
still works today.  You can find them used on eBay.  It operated by
eliminating transients above a certain slew rate and patching the
interrupted waveforms together.  It was not good at eliminating "hiss".

2.  Phase Linear (at the same time) made the Model 1000 noise reduction
unit.  This was an autocorrelator which filtered out hiss and rumble
and other quasi sine wave noises.  It basically separated the stochastic
noises from the music.  It did not work with sharp transients.  It is
also sold often on eBay.

The two together are quite effective.

3.  I have a modern commercial unit that does the same thing but you
really don't want to go there because of the really really high price.

Removing noise for transfer to CD:

I use Cool Edit to do the same thing with a computer.  I play the vinyl
disk through a pre-amp into a "Line In" on the soundcard to make a wav
file.  I open the file with Cool Edit.  I tell Cool Edit to "listen" to
a two second period of noise only, usually the lead in grooves, or
silent transitions between musical sections.  Cool Edit does a Fourier
analysis of the noise and constructs a filter exclusively to eliminate
this noise.

The results are amazing.  I have some old Caruso 78's that got this
treatment.  It is an astounding effect.  Before Cool Edit: plenty of
hiss; afterwards: the hiss is inaudible.

The next step is to play de-hissed Caruso back through a reverb unit
(Alesis midiverb4) to create another .wav file.  The reverb is necessary
for recordings made before modern microphones.  It adds nothing to
later recordings.  I then collect the .wav files and burn a CD.

Treating the vinyl surface:

I've tried lacquers and detergent and magic cloths and brushes and many
other things with no good results.

The one problem that I cannot eliminate is intermodulation distortion
associated with badly damaged grooves.  Sometimes when the hiss and the
like are gone the recording still sounds bad because the grooves are so
damaged that the stylus will not track well.  If it's a particularly
valuable recording I will experiment with pressure and needle diameter
and offset and whatever, but usually with little benefit.

I did try optical tracking where I measure reflected light modulated by
the groves.  This sounds like a good idea but it is always more noisy
than a stylus.

Anyway, this is my experience.  If it were me I would use Cool Edit
or similar software to do the job and transfer to CD.  That really
works best.

Bill Finch

 [ I'm very pleased with Cool Edit 96.  Later versions have added
 [ features which I don't need.  I think the digital filters are
 [ very well implemented, and so I assume the easier tasks are, too.
 [ Visit
 [ By the way, when I installed a new Pentium motherboard I
 [ experimented with the built-in sound capabilities: the on-board
 [ analog-to-digital conversion is distorted and noisy.  A plug-in
 [ sound card such as Sound Blaster works better.
 [ I suspect that the distortion is due to coupled noise from the
 [ nearby CPU that adds phase jitter to the A-to-D sampling clock,
 [ and that increases the IM distortion of the converted signal.
 [ -- Robbie

(Message sent Tue 5 Jun 2001, 18:08:05 GMT, from time zone GMT-0500.)

Key Words in Subject:  Disc, Noise, Old, Phono, Recordings, Removing

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