Re: Oscilloscope trace of sound signal


Chris Uppal wrote:

<snip testing and configuration saga>
.....
I tried all of them, and in each case ended up with the same format as above
(even the "mono" mic was stereo). Selecting the "Stereo out" option seems to
connect the input to the current output (why?) and -- at last -- your program
showed the current sound output.

I missed that bit in my original reading, and have been working
under the assumption that the problem was signal levels..
(shrugs) in any case, I made some significant changes based on
the results of a second PC that had 'amplification issues' ..perhaps
this version might work better for you.

(It is a worry you had to go that deeply into system config. to
see anything though..)

My message (prepared off-line) is..
Current traces calculate the audio level by looking at
the large order byte, ignoring the small order byte
completely. *

There are some significant changes to the audio trace
code, mostly based on the fact that a third machine
displayed results very similar to what you described.

Most significant in the changes is that the visual
'gain' of the signal can be configured,
http://www.physci.org/test/oscilloscope/screenshots/sinetone.png
the screnshot shows a gain of 1 as it displays the signal
generated by the 'Audio Tone' jar to it's left.

Audio Tone is a jar here,
http://www.physci.org/test/oscilloscope/tone.jar
it generates a more predictable signal - a simple
sine tone with a harmonic (if you want).

The default volume is 20% (for good reason), but for these
screenshots I ramped it up to 90% volume.

I suppose you, Chris can especially appreciate how different
this will appear at gain 1 on your system. (Having seen it
on the 3rd PC, I can vouch it is - quite oddly boring).

I am guessing you'll need to push the gain beyond 7
(the default is 5) before you see a trace ranging this big,
and then it will be very blocky. *

Second, now there is an option to DisplayEachByte** of the four
bytes in each audio frame.
http://www.physci.org/test/oscilloscope/screenshots/sinetoneallbytes-a.png
The size of the small order bytes
has been knocked down to 1/8 the display height at 'gain 1',
by gain 8 it should be clipping.
http://www.physci.org/test/oscilloscope/screenshots/sinetoneallbytes-b.png
Here's a screenshot of 'all lines' showing a gain of 1 and seven
in the separate trace panels.

** The reason I added this option is because I cannot for the life
of me figure how to combine these bytes with the larger order
bytes in any sensible way.

* Which has become especially important since most of
the audio trace detail of two of the three PC's tested,
lies in those small order bytes.

Increasing the gain can amplify the visual trace to the
point of doing something interesting, but I need the small
bytes to give the trace any detail.

BTW
- You can click the trace(s) to toggle the gain
through 15 and back to 1.
- All the screenshots were done with a fade rate
of 100% (clear old traces) in order to simplify the image,
the default is a slowish fade for each trace - much prettier.
- the byte conversion has been shifted to the
'frameToSignedDoubles' method (bottom of AudioTrace source)
- Tooltips galore - most notably on the entire Visual Gain
and All Bytes panels.
- The default settings are visually complex. To simplify the
trace, flip the default values of the check boxes and increase
fade rate to 100%.
- All files available from
http://www.physci.org/test/oscilloscope/

Andrew T.

.

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