At 6:17 PM +0000 6/15/10, Bocianowski Thomas wrote:
> Hi All,
>
>I have recently started to record sounds around, first using a voice
>recorder, then I decided my self for a Marantz PMD 620.
>By now I am recording at a lower level of gain to limit the unwanted noise=
.
>
>In fact if possible I'd like to have some advice on how to record
>properly, I searched the archive but couldnt find resources on that
>particular recorder, but I guess there are general rules that could
>apply.
>
>Shall I use only PCM or MP3 can be sufficient ?
>Is there any particular software that can help in removing
>hiss/unwanted noise ?
>
>Thanks,
>
>Thomas
=3D =3D =3D =3D
Hi Thomas.
Thanks for scanning the archives first!
Even though it has a profound impact on "quality," I didn't fully
understand the sources of noise in recordings for many years. Its not
a particularly complex phenomenon-- just not what it first seems to
be.
In the great majority of instances, the source of noise one hears in
recordings is the "self-noise" of the microphones used. When you
increase the record gain in the recorder, it seems like this
adjustment is adding hiss or noise, but its really just the signal
from the microphones being amplified and becoming more audible along
with the audio signal subject matter.
The ratio of the mic "self-noise" to the audio signal is pretty much
a constant. If you use a lot of gain the combined self-noise and
audio signal has more "level" or "saturation" on the recording
medium. If you use a small amount of gain, the combined self-noise
and audio signal has little "level" or "saturation" on the recording
medium. To hear the high level recording at a comfortable level, you
might have to turn the playback volume down. Conversely, to hear the
2nd recording at a comfortable level, you might have to turn the
playback volume up. As long as you don't turn the record level in
the field so high that the audio signal overloads the record circuit
and distorts, the amount of hiss or noise in the audio played back in
both recordings will be very close to the same. There are two more
common exceptions. The mic preamplifier circuits in lower cost
recorders can add some more noise at the highest settings and if the
signal is recorded at a very very low level, there can be additional
quantizing noise. A good rule of thumb is to set the record level so
that the "peaks" of the bird calls, music, voice, etc. extend into
the range between -25 and -12 dB on the record scale. Feel free to
use whatever record gain is necessary to achieve this level without
significant quality loss. There are other caveats, but these
principles are good one's to "lock-in to one's memory" before
exploring them and becoming confused again.
As far as tricks to achieve very low noise recordings, none are as a
effective as using mics with very low self-noise. As a guide, the
built-in mics in your PMD 620 probably have self-noise in the range
of 25dB(A) to 32dB(A). Mics that folks use to reduce noise to the
lowest levels have about 1/4 to 1/6 as much noise with self-noise
ratings in the 5-10 dB(A) range. As a result, one has no trouble
finding posts in the archive with the terms, "low self-noise mic
cost" in common. ;-) Rob D.
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