[sdiy] Measuring Audio Sine Purity

[Paul Perry]

I'm not sure that THD is always the most appropriate measure, when it comes 
to judging a DIY synth sine wave.
For example, I have made saw to sine converters that sounded pretty good, 
and doubtless would have measured resonably well - but had spikes at the 
crossover points that were pretty unfortunate at very low frequencies, when 
using the sine as a modulator.

All I can suggest, is that since the distortion artifacts are always going 
to be multiples of the fundamental frequency, you might get some indication 
by building a band pass filter set at say 1KHz, and seeing what came through 
as you tuned the oscillator to submultiples - 500Hz, 333.3, 250 etc.

paul perry Melbourne Australia

----- Original Message ----- 
From: "Scott Gravenhorst" <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, September 08, 2012 9:56 AM
Subject: [sdiy] Measuring Audio Sine Purity


>
> How would a DIY person measure the purity of a sine wave beyond using a
> spectrum analyzer?  To give a figure of sine purity, of distortion (THD?) 
> ?
>
> Say you have an oscillator you built, it's supposed to be a sine 
> oscillator
> and you'd like to know just how pure it is.  What would you use?
>
> I've used RMAA to analyze a wav file of a sine signal, but that doesn't
> give purity numbers, it just gives the spectrum.
>
> Is there software that might be used with a good sound card?
> (understanding, of course, that soundcard artifacts will present 
> themselves
> in the results)
>
> I imagine that there is expensive hardware, but that's out of the question
> for me.
>
> -- ScottG
> ________________________________________________________________________
> -- Scott Gravenhorst
> -- FPGA MIDI Synth Info: jovianpyx.dyndns.org:8080/public/FPGA_synth/
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