Hi Laura,
You said,
"My files were recorded as MP3s, with a 44.1kHz sampling
frequency and 16-bit sampling rate."
That would be the default setting for a PCM (.wav) file, but not for an MP3=
. PCM files are usually described in terms of bit depth (e.g. 16 bit or 24 =
bit) and MP3 files are described in terms of bit rate as kilobits per secon=
d (kbps) which is not the same thing as bit depth.
A stereo PCM file at CD quality is 16-bit, 44.1 khz, which works out to a b=
it rate of 1,411 kbps (16 x 44.1k x 2). A mono PCM file of the same quality=
would be half that, 705.6 kbps.
If the long sample you uploaded to soundcloud is representative, you have b=
een recording mono MP3s with a bit rate of 32 kbps and a sampling frequency=
of 44.1 kHz.
32 kbps is the lowest bit rate available on the PMD for recording mono MP3s=
at that sampling frequency. There may be other issues, but starting with a=
low-resolution version of a compressed recording format is one of them.
I just hope you are able to work with the recordings regardless!
John
--- In "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 pictur=
e). 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 w=
ill 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 d=
o 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 manua=
l)? 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 ex=
actly like what I am experiencing, with the white shadow eclipsing the back=
ground noises in high-volume (or perhaps it is related to high frequency) s=
ounds.
>
> If it has to do with aliasing (as I understand it, sounds that are over t=
he Nyquist frequency are distorted upside down somehow), then Raven has a l=
ow-pass (anti-aliasing) filter. I'll experiment with that and see if it cha=
nges 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 embar=
rassed to say that it's a problem I'm stuck with, as that was the default f=
ile format, no one mentioned that it wouldn't be good enough, and I didn't =
know enough to change it.
>
> Laura
>
"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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