Re: [ARSCLIST] Non-RIAA preamp

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 10/09/06, phillip holmes wrote:
> In the phase encode/decode discussion of RIAA, did anyone mention that
> speed is critical? If the disk was recorded slow or fast, you'll have
> a hard time getting proper frequency response. 

Playing at the wrong speed affects pitch, but not really frequency
response.

> And many older playback
> decks ran slow or fast, again making the frequency response and phase
> wrong. But the absolute worst is off centered pressings that cause a
> constant change in phase and frequency response. 

Constant change in pitch and phase.

> Makes me sick on
> really bad ones. AND, many RIAA stages are off by at least 1dB. 

That, OTOH, does affect frequency response.

> If you
> compound all the errors, it's enough to make you listen to MP3. Oh,
> let's not forget tangency error, groove pinch.... It's a wonder they
> sound as good as they do. The best solution for these problems would
> be to play back on a Nakamichi turntable (automatic disk centering)
> and introduce RIAA in the computer. Sadly, I don't have the Nakamichi
> table. But can't you fix the speed in the computer, then do RIAA? I'm
> going to get someone to show me how to do that one of these days.

Fixing the pitch is a matter of scaling the recording to be shorter or
longer.  It is ften labelled "resample".

If you try scaling some images in Photoshop, you will see what the
problem is: the image becomes slightly blurred. Increasing the sample
rate helps here (or increasing the resolution in an image), so if you
plan to correct speeds I would record at 192 KHz.

I don't know of software for correcting off-centre discs but it probably
exists.

Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx