| Application
note # 5 |
Sample
Champion
|
Using
square and ramp signal types
Sample
Champion main purpose is MLS analysis, but the signal generator
can synthesize and play also pure tones, square and ramp waves.
These signals can be useful for many kinds of acoustical analyses
and also for testing the sound card itself.
When
selecting the square wave signal type, the generator
will play a square signal at the selected frequency only
for half of the sampling time. This has been explicitly
designed because the input and output lengths are 2^N -1 samples
long and it was not possible to generate a square wave with
this length and with the right harmonic content. But
this is not a problem when analyzing a measurement of this signal:
the trick is selecting an input buffer length 2 or 4 times longer
than the FFT size.
For
example a setup could be (see figure):
- Square
signal of the desired frequency
- Input
length 16K
- FFT
length 8K
- Full
Blackman-Harris weighting window
- Average
64 cycles
The
"Selection A" starts from the first sample and ends
on the last sample of the square wave.
IMPORTANT:
it is recommended to avoid the use of an external signal generator
when the average feature is enabled because this could cause
wrong results.
Another
useful signal generated by Sample Champion is "Ramp".
This signal is a series of small portions of square wave with
amplitude varying from 0 to +/-2^15, each of them has amplitude
2^K where k=0..15. This signal is designed for testing the monotonicity
of the D/A and A/D converters of the audio device.
To see the least significative bits, just zoom the Y axis.
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