Hi Laura,
I downloaded both your files from SoundCloud. Listening to the
longer file I would say that the quality is appalling and unuseable
for any research purposes. I am surprised you were sent out to do
field work without either having someone set the recorder correctly
for you, or showing you what you needed to do. You should have been
monitoring the sounds you were recording through headphones, then you
would have known something was wrong right from the beginning.
In analyzing what has gone wrong, I see that the audio frequency in
both files only goes as high as 6.6 kHz, while the birdsong is
starting at around 4 kHz and would have included sounds higher than
Message: 6.
Subject: 6 kHz. Hence, apart from any overload problems, much of the
birdsong is simply not in the recording.
Such a low sample rate would be caused by using either a very low
quality setting in the mp3 format and/or and sample rate of less than
16 (should be 44.1 or more).
When you are looking at a sonogram of properly recorded birdsong, you
should be seeing a window that shows sounds up to 22 kHz.
Vicki Powys
Australia
On 17/07/2012, at 7:18 AM, laura.hilberg wrote:
> Thank you all so much for your suggestions (and experiments)! It's
> a huge relief to have a community of people who really understand
> this stuff.
>
> I uploaded a short recording of a single song (the same one in the
> picture). It is on SoundCloud, and the URL is http://soundcloud.com/
> laura-hilberg/nesp-song-short-clip. I made it public and
> downloadable, so hopefully it will work for everyone. I also
> uploaded the complete, unmodified sound file (about 10 minutes),
> which is at http://soundcloud.com/laura-hilberg/6-12-12-bhm-nesp-11.
>
> To try to answer some of your questions:
>
> 1) I am absolutely sure that the automatic gain was turned off.
> What this meant was that I adjusted it manually for each recording,
> trying to ensure that the gain was high enough to pick up the sound
> but not so high that it went over. I'm not sure if this is the same
> thing as 'fixed gain', but I do know that it was adjusted manually
> only.
>
> 2) The limiter was turned off.
>
> 3) Is clipping the same thing as aliasing (referred to in the Raven
> manual)? If so, then I know what you're referring to, but if not
> then I'm still not sure what exactly that is. John, your experiment
> with the fan sounds exactly like what I am experiencing, with the
> white shadow eclipsing the background noises in high-volume (or
> perhaps it is related to high frequency) sounds.
>
> If it has to do with aliasing (as I understand it, sounds that are
> over the Nyquist frequency are distorted upside down somehow), then
> Raven has a low-pass (anti-aliasing) filter. I'll experiment with
> that and see if it changes what I see. I know the low-pass filter
> was turned off on the recorder, so perhaps this is the problem.
>
> 4) My files were recorded as MP3s, with a 44.1kHz sampling
> frequency and 16-bit sampling rate. Perhaps this is the problem...
> if so, then I am embarrassed to say that it's a problem I'm stuck
> with, as that was the default file format, no one mentioned that it
> wouldn't be good enough, and I didn't know enough to change it.
>
> Laura
>
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