Ray wrote:
> but I wonder if we've managed to overwhelm Laura?
> There's no sign of her... I hope we haven't scared her off!
Yes, maybe there have been too many experts posting their odd opinions ;-)
But to get serious, I believe that probably not much is lost for Laura's
dialect study on the Nelson's sparrow as long as it was sufficient to examine
frequencies below 6 kHz.
One of the recordings on Xeno canto however may indicate that this species
sometime produces syllables (short click-like sounds on
http://www.xeno-canto.org/55205) that are entirely above 8 kHz.
For a better frequency resolution on the spectrogram display I would recommend
to first down-sample the recordings to 22.05 kHz (or even to 16 kHz because the
low bit rate mp3 setting already removed anything above about 6 kHz).
Because there are probably no syllables below about 1.7 kHz, it would be safe
to just ignore any signals below that frequency (the background noise floor
that is partly affected by the lossy mp3 compression is nor relevant for this
study). In order to facilitate this, it might be useful to high-pass filter all
the recording at that corner frequency. Some sound analysis applications also
allow hiding certain frequency intervals.
In case the dialects should be classified visually based on the spectrogram
displays, I would recommend to adjust the display contrast in such a way that
only the song without the background noise is visible.
Here is a spectrogram image created with the free Avisoft-SASLab Lite software,
along with the settings that I believe are appropriate for this kind of
analysis:
http://www.avisoft.com/scratch/dialect%20study.pdf
Regards,
Raimund
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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