Hi, I just made some impulse response and distortion measurements on the speaker->microphone path. The measurements are shown in figures http://people.xiph.org/~jm/olpc_distortion.png http://people.xiph.org/~jm/olpc_distortion2.png
Both figues have the same data. The only difference is the frequency axis: first figure has the frequency of the harmonic on the horizontal scale, while the second one has the frequency of the fundamental that caused it. e.g. for a 1 kHz tone, you need to read the harmonics at 2, 3, 4, 5 kHz in the first figure, while for they're all aligned at 1 kHz in the second one. (second figure is easier to read) The main things that strike me from these figures is that there are resonances in the fundamental around 3-6 kHz and which cause quite a bit of harmonic distortion. The distortion is also especially significant because it happens at a "normal" volume. It's measured using a sine sweep from 40 Hz to 24 kHz as explained in: http://pcfarina.eng.unipr.it/Public/Papers/134-AES00.PDF The sine waves were nearly full amplitude and the alsamixer volume for Master and PCM were both set to 61. In case anyone's interested, the raw data is available at http://people.xiph.org/~jm/response and requires the paper above to interpret. I'm still not sure what can (or can't) be done to improve the situation. Any thoughts? Oh, and I was just wondering, what kind of microphone is the BT2 using (omni, figure-of-eight, cardioid, ...)? Cheers, Jean-Marc _______________________________________________ Devel mailing list Devel@laptop.org http://mailman.laptop.org/mailman/listinfo/devel
