From:
>
> This is a question that has been plaguing me. I record in stereo from a m=
ono
> microphone so that if I have a sudden increase in volume from the subject=
I am
> recording the high trac will "Clip" or "burn out", but the low trac will =
not.
> However, I have noticed that when the "high" trac is fine and not burnt, =
the
> low trac does not seem to have the same quality. I use an HHB Portadisc M=
D.
> So, my question is...at what -dB will the machine start receiving too lit=
tle
> data to capture all the sound. When something is recorded at -60 dB once =
it is
> equalized with something recorded at -10 dB will they sound the same (and=
look
> the same in a spectral analysis)? My experience says NO. So, there must b=
e some
> range of -dB where the machine is just not getting enough data to capture=
the
> sound. Any idea what this -dB figure is?
>
> I know that the above sounds pretty unscientific and unsophisticated, but=
> please be patient with us scientifically impaired recordists!
I don't know if I understand the question, and only comment about what
works for me, but here goes.
I don't know about using the word scientific around this sort of stuff.
There is some science theory, to which I refer you to "The New Stereo
Soundbook", but a great deal of this is pure opinion on what sounds best
to a given individual. And groups of individuals have group opinions too.
There is certainly no rule that says that both channels of stereo have
to be the same volume all the time. You are not trying to get the two
stereo channels to sound the same. It's the differences that make it
stereo. Effectively the center of interest moves around in the field
during the length of the piece. In nature recording often more than in
studio recording. And Psychoacoustics tells us there is interchannel
masking going on as well. So, the quiet channel does not have to be the
same quality as the currently dominant channel.
If your software can use the plugin, download Inspector:
http://www.elementalaudio.com/products/inspector/index.html
Look at it's balance meter while playing a stereo recording, you will
find that sounds come and go on both channels. Note if you use Peak in a
mac and are up to date it's already in your plugin list. Read the
documentation in inspector about centering the field. You cannot exactly
center the field all the time and have good stereo.
One of the cues that makes the stereo field is differences in volume.
You should not be equalizing the levels of the two channels in post, but
make sure you have the gain set to the same when recording. (assuming
you are recording with two mics of the same model) And set your gain so
you have headroom on both channels. If you have to shift the gain during
recording, shift both channels. On average I set the Portadisc for the
steady "regular" sound level I have to indicate at about -15dB, but if I
think it might be a site with some extremes, I'll go lower.
In the same vein you don't want to filter the two channels so they sound
the same in other ways either. That would almost certainly destroy some
or all the cues that create the stereo image.
I record my stereo with two mono mics, mics are mono, it's the combining
of them that makes stereo. The stereo field is largely created when I
record, though with M/S I can do a fair amount of modification of it's
width. Recording in pseudostereo, lots of mono mics all located by
panning in post, is a different animal. There you would worry about each
mic getting the same level readings. You do this in the two mic setups
when the two mics differ, like they usually do in M/S recording. There
you do set the levels independently initially when recording the
undecoded M/S. Actually M/S can be tricky about that, sometimes the mid
mic will be getting more volume from a site, and sometimes it's the side
mic. So you set for each site, not just for the model of mic.
For the Portadisc, the meter reading that it would stop recording all
together is about -94dB. There are some 65,000 possible levels between
that and 0dB. That's the dynamic range of the recorder. Few natural
environments will have near that kind of dynamic range. More typical
would be 40-50dB dynamic range to be recorded, or less. Even ignoring
the fact that some of that range would be above my -15dB setting, a 50dB
dynamic range site would have it's softest sound coded at -65dB, nearly
30dB of unused range on the low end.
There are those that worry that sound levels will not have enough detail
in the lower levels, but that's quite a way down. I've cranked in
30-40dB of gain into a quiet recording in post and everything I hear is
still plenty good. Since I'm a old style recordist and don't like
banging the ceiling, I rarely push my stuff higher than the max peak at
-2dB, and to do that would normally take less than 10dB gain, and often
far less. My software gives me the peak sound number automatically, so I
can easily avoid pushing things too high. Or find out the bad news that
I managed to clip somewhere when recording (often that's when a car passes)=
.
Note if recording in a very quiet site that's not going to have any
sudden outbursts I'll still set my gain at the -15dB level, which
amounts to a lot more gain than a louder site. Typically, quiet sites
have very low dynamic range, so now most of the recording will be at the
top of the range. When you get into post is where there is some
difference of opinion how to handle quiet site recordings. Some keep the
gain up, some, on the theory it's quiet let the level down a ways. The
real trick is you want to keep the listener happy, you don't want them
to be constantly feeling like they need to adjust the volume. That means
knowing your listeners, tricky.
Walt
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