[time-nuts] Oh dear

[Poul-Henning Kamp]

In message <4FA80913.7000703 at medesign.ro>, MailLists writes:

>That was a big problem with the dynamic range of tape recorders, which 
>had to be solved with noise reduction circuits. Even good 16 bit ADCs 
>have a higher DR than the SNR of most instruments in quiet recording 
>studios.

Not so fast there...

Yes, in theory your ADC could digitize a signal 14*6 = 84 dB below
reference level, but it would do so with 50% distortion, because
there would only be three distinct levels: {-1, 0, +1}

This is a much overlooked issue, in particular with classical music
where dynamics in the music can account for way more dB than people
realize.

We must start out by defining the acceptable level of total distortion,
if we choose 0.5% then we need 200 digital levels, roughly 8 of
your 16 bits for the signal.

That gives you a headroom of 7 bits (leaving one for the sign) and
that gives you 42 dB of S/N.

That isn't very much, headroom, 42dB, when the conductor waves the
entire philharmonic AND the full opera choir in, for for that wonderful
"Dies Ira" of Verdis.  Or Carmina Burana.  Or any of the many
other 'shock-effects' classical composers have enjoyed.

With digital, you get most distortion at weak signals, where your
ears are much better at detecting it, with vinyl you get more
distortion on strong signals, just like your ears, meaning the
level becomes unbearable sooner.

That is why, in plain and simple terms, classical struggles with
digital:  High distortion in weak passages.

It is also why the CD media has changed rythmic music, which
went from a love of distortion to a love of pure tones when
the CD media made it possible to play loud pure tones.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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