Hi Laura,
I could not access your SounCloud files for some reason. But nevertheless, =
from what you say below I am willing to bet the problem is in the MP3 compr=
ession. Such visual(but not necessarily heard)artifacts are common with MP3=
. If the sound is loud enough, the quieter frequencies above and below it a=
re somehow removed to save space.
If you can, it is best to record in wav format at a minimum of 44.1kHz/16bi=
t resolution. If you must record in MP3, use the highest bitrate available.=
Any bitrate less than 128kbps is likely to exhibit audible artifacts.
John Hartog
rockscallop.org
--- 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
>
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