linuxaudio.org

(sorry Harry, I missed to CC the list)

On 12/21/2011 03:29 AM, Harry van Haaren wrote:

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> Hey all,

>

> I've been writing a scope the last while, and I'm intrested in how other

> people have approached plotting the data.

http://kokkinizita.linuxaudio.org/linuxaudio/downloads/yass-0.0.2.tar.bz...

or http://xoscope.sourceforge.net/
> Currently I'm taking every 50th sample, and drawing a line from the

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> previous sample to there, and so on. Not particulary neat.

> So is there a resample, or smoothing of the samples, or how does one plot a

> "smooth" waveform like Ardour / QTractor?

IIRC ardour uses all audio samples and lets cairo do the scaling.
> My other question is about RMS, is calculating it in its literal sense

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> best?

It depends on the use-case. A traditional analog scope does that. Well,

it is not true RMS but a low-pass filter.
>Or perhaps only taking every 5th sample?
Better take the min/max of all sample that fall on a single pixel on the

time-axis and draw a box (actually a vertical line if x is the time-axis).
> Resampling the signal from 44.1 or 48k to say 11025? I'm not really sure

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> which way to go.

11025?

25 (fps) (or actually: screen update-freq aka vblank-frequency)

multiplied by the width of display in pixels is more appropriate.
Cheers!

robin

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