I downloaded the lite version for a look at the spectrograms, and I think
they're useful, but are limited by poor presentation. It's exciting that
they're included, but they need work. I hope our local apps, Morcombe/Stewart
and the forthcoming Pizzey and Knight/? include these sooner rather than later.
They seem to have applied some kind of noise suppression or compression to the
recordings before generating the spectrograms, which results in areas of
complete black between notes. But the background "noise" is present during the
notes, so you get these confusing vertical blue bars, which should be ignored.
You need to concentrate on the green bits only.
I'm thinking they've quantised the values into just high, medium and low
(green, blue, black), rather than display a continuous range. This makes the
loudest bits stand out, but hides the softer detail. I think it would have been
better to just use a full greyscale.
Every track's spectrogram fills the width of the screen, so the time scales
aren't consistent, and there are no times shown, just four pointless,
identically placed tick marks on the time axis.
The frequency scale seems to be identical for each call, which allows
comparison, but hides the detail of the lower pitched calls. There are no
frequency labels, it just says "kHz". They could have made them much taller -
they're so squashed that they lose a lot of detail. I think this alone would
make a huge difference to their usefulness.
I find a well presented spectrogram to be invaluable for understanding a call
well. These are better than nothing, but could be much better.
I wasn't able to find a way to start and stop the tracks playing, so I had to
resort to turning the volume right down while I looked at several spectrograms.
They just start playing as soon as you go into that section, whether you want
it or not.
The spectrogram settings are just three quality/speed settings. These don't
seem to affect the speed of spectrogram calculation on my recent iPad model,
but might on an older one. They make the spectrograms look different, but I'm
not sure what they do. If they affect speed of calculation they might control
FFT window size or overlap.
It's interesting that they've included these controls. It means that the
spectrograms are generated at the time of playing. This means that they could
potentially give you control of more parameters like the quantisation and
scales. I would have thought they would have carefully generated them
themselves and stored them as images. I suspect someone has decided at a late
stage to include spectrograms, and has just set it up to auto generate them all
with the same parameters. If you could control more parameters, and could save
them for each track, this would be a great leap forward in the presentation of
bird recordings in apps, in my opinion.
There's a good tutorial on reading spectrograms at
http://earbirding.com/blog/specs. The Canyon Wren spectrograms at
http://earbirding.com/blog/specs/pitch-and-inflection can be compared to those
in the lite version of the app to get an idea of how much more useful they are
when done well.
Peter Shute
Sent from my iPad
On 08/02/2013, at 3:46 PM, "David Adams"
<<>> wrote:
iBird, by
the way, also includes spectrograms for the bird calls. I'll admit I
haven't read up on how to make use of these, but they sure look great. As I
understand it, there's a technique for using to better memorize and recall
bird calls. Even without knowing what exactly they're all about, they're
interesting and you can easily "see" the call. Many of the on-line
recording libraries seem to be heading in the direction of including such
graphs with recordings.
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