RIAA phono eq curve

[Eric Hedekar]

On Wed, Mar 18, 2009 at 9:31 AM, Phil <phil at magnustudios.com> wrote:

> Hey,
>
> I've got a large collection of vinyl records I need to record onto CD, or
> some other digital format. I've got a stereo with phono inputs, so I could
> use that for the preamp, but I'd rather take the phono player directly into
> my firebox and correct the EQ digitally.
>
> I've done a bit of research on what I need to do. I need a really accurate
> diagram of the RIAA phono curve. The best I've found so far is the one at
> wikipedia, http://en.wikipedia.org/wiki/File:RIAA-EQ-Curve.svg . It's only
> got the markings for 20, 1000, and 20000 Hz. I guess it's got to be a
> logarhythmic graph so I should be able to use it to acurately find the other
> frequency levels.
>
> What I'm hoping for is that someone has already done this and has made a
> preset for a ladspa plugin, or for jamin. Does anyone know of this?
>
> If not, I'll make mine publicly available when I do it.
>
> Thanks,
>
> Phil
> phil at magnustudios.com
>

Hi Phil,

Three things jump to mind:
1.) I recall hearing something about some open source DJ software (I think
it was either DJPlay or Mixxx) that has the option to bypass the digital
player and just send the turntable output to the stereo (instead of the
vinyl timecode control playing the digital file).  In this, I recall that
there was a RIAA phono curve in the bypass chain, so one could theoretically
set this software in the chain between one's turntable and audio recording
app to get the proper attenuation - I think.
2.) That graphic is an SVG, so if you need to, you could take the red path
element:

    <path
       d="M -995.55172,-101.99092 C -864.5242,-89.793364
-795.73132,10.259811 -669.39874,40.066541 C -543.06615,69.873271
-442.55816,174.6187 -422.25595,183.30485"
       style="opacity:1;color:black;fill:none;fill-opacity:0.20238097;fill-rule:evenodd;stroke:red;stroke-width:3;stroke-linecap:butt;stroke-linejoin:miter;marker:none;marker-start:none;marker-mid:none;marker-end:none;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1;visibility:visible;display:inline;overflow:visible"
       id="path2995" />

and only pay attention to the d="snip" portion to extract the exact bezier
curve that the line follows; M stands for starting point, then the numbers
after each C describe a differnet bezier curve (read more info here:
http://www.w3.org/TR/SVG11/paths.html#PathDataCubicBezierCommands ).  But
keep in mind (you already mentioned it) that it's a logarithmic graph.

3.) A phono signal into your Firebox might not be the best signal to noise
ratio for recording.  You might just be better off to go to your local
electronics store and buy a $20 phono preamp to stick in between.  Maybe
your research has proven this gut thought wrong, but it is going to force
the firebox's noise floor up 46db (though that shouldn't be that horrible).

-Eric

-- 
_______________________________________
    http://greyrockstudio.blogspot.com
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