Re: [ARSCLIST] Advice for filtering surface noise

[Goran Finnberg <mastering@xxxxxxxxx>]

Don Cox:

> > 1 .) If you aren't using a device that uses the stereo signal for
> > noise cancellation you MUST play the records in mono or else you are
> > inducing an order of magnitude more noise than you would in mono.
>
> The ratio is root 2 - that is, 41% more.

This only holds for equal valuse of broadband noise in the vertical and
horizontal directions.

Ie the wanted audio mono signal is correllated between left and right
and the noise is uncorrellated so when summed L+R = M gives a + 6 dB
increase of the wanted signal while the uncorrellated parts only adds to
give + 3 dB increase for a net gain of + 3 dB for the wanted signal
your:

> The ratio is root 2 - that is, 41% more.

In a normal disk replay chain using a stereo cartridge one have to deal
with the fact that the cartridge compliance is different between verical
and horizontal so the cartridge compliance - tonearm mass low end
reonance sits at different frequency between vertical sensing and
horizontal and shows different Q and peak lift and this will quite
markedly effect the amount of less garbage seen when monoing any disk.

Also most disks especially shellac ones are not particularly flat so the
ampunt of vertical excitation can be very high.

It´s not unusual to see gains from 6 to 10 dB when monoing shellac
disks.

A highly non flat shellac disk some monts ago gave something like almost
20 dB reduction in LF warp exitation a month ago when monoing so an
order of magnitude is fair to state.

So when I see anyone talking about sensing only left or right channel to
have lowest noise then this is wrong.

These disks should always be replayed in mono for best transfer.

BTW, also the replay distortion due to pinch effect is an order, or
more, of magnitude lower when monoing.


--
Best,

Goran Finnberg
The Mastering Room AB
Goteborg
Sweden

E-mail: mastering@xxxxxxxxx

Learn from the mistakes of others, you can never live long enough to
make them all yourself.    -   John Luther