Re: [LAU] Sampling an external oscillator waveform

From: Fons Adriaensen <fons@email-addr-hidden>
Date: Wed Feb 11 2015 - 23:39:40 EET

On Tue, Feb 10, 2015 at 09:22:10PM +0100, F. Silvain wrote:

> >The 'correct process' requires just common sense and maybe
> >some maths to explain it. If you are unmotivated to the
> >extent suggested by what you write, just drop it.
> False place for being economic with words: I'm self taught
> and thus not sure of how far I can go with the allowed spare
> time.
> As I accidentally mailed off-list: a friend can offer a digital
> oscilloscope with a samplerate of upto 1gHz, but with only 12bit.
> It can sample and output data in different computer readable formats.

Some sense of proportions could help here. That 1 GHz sample rate
is quite useless. You'll get a better result capturing the waveform
using an ordinary sound card and whatever recording SW you prefer.

The same is true of the 65536 samples wavetable. The *only* reason
for using such a long one would be that it allows the synth SW that
will be using it to just pick the nearest sample instead of using
interpolation. You'd get the same if not better quality using say
1024 samples and even some even simple interpolation scheme.
 
> I'm open to learning new ways. Only I passed my A-level in math,
> furthered by some audio related reading in the recent past, which
> is the reason for my hesitation.

What you want to do doesn't need rocket science, but it requires a
good understanding of the basics. And it's certainly not something
you'd want to do 'manually'. But there are no standard and easy to
use simple tools that I know of that will do the job.

It wouldn't be too complicated to write some relatively simple
python/numpy code that would capture the analog signal or read
it from an audio file, find the exact period (which won't be an
integer number of samples), and interpolate it to whatever size
you need. If you could send me a few seconds of the recorded
signal (at some relatively low frequency, around 100 Hz or so),
I might be tempted to have a go at it.

Ciao,

-- 
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
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Received on Thu Feb 12 00:15:02 2015

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