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Section 9
Noise Elimination
Be careful though, remember that peak limiters, limiters,
and compressors can alter dynamic ranges to give this sort
of pattern. It is best to check for clipping without these
devices in the way if you can.
In the wave editor it was very noticeable that although I had
a nice loud signal there was a significant clipping at about
95%. As I just said, this is indicative of driving the card too
hard. But the clip indicators didn't show. Well, that's
Cakewalk for you.
Whilst Sound Forge still doesn't show clipping, I used it to
monitor the setting up of record levels, as SF gives the peak
as a figure not just a meter (you have peak hold!). Here SF
showed a peak at -0.4dB. Seems to be a bit tight. Indeed on
playback clipping is evident. I reduce the Master Out fader
on the mixing desk (the real one not the Cakewalk one!) so
the peak is now at -2dB. Don't worry about changing the
levels in the Volume Control dialog box in windows—If
you are driving the card too hard it won't matter what you
do on windows.
So I turn down the master fader. Most of the problem has
been alleviated. But even with a max peak at 87% there
appeared to be several peaks that looked 'chopped' at this
limit. I am still suspicious of a clip. Indeed, with this
particular piece I am playing it is around these bits that the
monitor speakers show some kind of distortion/rattle.
Hmm. There is so much headroom that it can't be the
mixing desk output, and the mixing desk certainly has been
correctly set up so its not clipping on the PC—it must be
elsewhere down the line.
At this point I checked the sound from the speaker
cabinets—did this clip? I don't think so. Now the difference
here is that the two signal paths split at my Palmer PGA-05.
So I turn down the filtered output levels—this affects the
level going into the desk. I check again and the clip is still
present. I reset the volume (no I didn't balance the desk for
the new level in case it was the desk input that was being
clipped). OK, so the next unit down the line is the GT-3—
hang on, this feeds both signal paths - the clip cannot be
here can it? I've checked the GT-3 meters and everything is
fine. OK. But you haven't got a meter showing the output
AFTER the external control knob. If you turn this to zero
the master output level which is shown on the meter
remains—it doesn't drop. Therefore you need to be careful
as you have no real indication of the actual output volume
from the GT-3.
Maybe I am driving the PGA-05 too hard. But how? Surely
the amp would amplify the PGA-05's problem. The trick
lies in the fact that, as I said earlier, the PGA-05 has a thru
jack and filtered outputs. If you switch the unit OFF the thru
jacks keep working. So I turn down the GT-3's level and re-
© Copyright 2000-2002 Barry S. Pearce et al.
record. The problem has disappeared from both the
recorded .wav and the monitors.
I can now set up the GT-3 so it doesn't clip the PGA-05, the
PGA-05 so it doesn't clip the desk and finally use the
Master Out fader on the desk to avoid clipping the sound
card.
Although you may not be running such a set-up, you may
have a similar set-up with a digital multi-tracker such as the
Roland BR-8 or a Tascam. The principles are basically the
same, the details just need adapting to your particular set-
up.
You can also help yourself avoid clipping by knowing and
understanding the technical specs of your equipment, where
equipment specifies max output/input levels and nominal
output/input levels you can see whether or not one unit will
overdrive another.
Phew. That covered a lot as well. I hope by now that your
system is now nice and quiet noise wise and additionally is
now free from clipping.
Please let me know if you have any further advice.
Especially regarding specific units you have had a problem
with which needed a slightly different solution than that
which I have described.
Noise Elimination—Recording
onto Computer
Well, this is going to be quite a quick follow up to our
discussions on noise elimination.
If you are recording near or onto a computer it is possible
that your pickups (especially single coils) will be picking up
a lot of noise. Most (probably 80-90%) of that noise will
come from the computer monitor. Thus whenever you can,
switch the monitor OFF. What I do is set the software
recording, obviously giving myself plenty of time before I
need to play. I then switch the monitor off – let the noise
subside and then start recording. When I've finished
recording I then switch the monitor back on. This can
eliminate a huge amount of noise.
Hi-Tech Noise Elimination
Many of you have computers with software such as Sonic
Foundry's Sound Forge. Did you know that SF comes with
a spectrum analyser? Even if you don't have SF then there
are a number of freebie analysers out there on the web. You
can use these spectrum analysers to assist in eliminating
noise rather than turning up volume controls. It is much
more accurate and you instantly get to see if something you
plugged in has caused a ground loop or not.
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