Table of Contents
Advertisement
up to 125% with 100% representing unity gain. The 125%
is in red. Samson state that its OK to have this light up
occasionally. Mine lights up a good deal more frequently
than I would like, although my system appears not to be
clipping. The transmitter level pot is at minimum. Yet I still
get the problem. The output volume control does not affect
this as it is after the air interface, and this is showing signal
level over the air interface. I found that my humbucker was
too close to the strings and was clipping the transmitter. I
have now altered my pickup height and the problem has
been resolved.
If you use an effects loop—or a loop of any kind...and I
don't mean feeding the GT-3/5 into the return when you
didn't use the send... Then treat this just a normal 'mini
chain', using the same approach as above. Before you do
however, place a cable direct from send to return—check
for clipping. Any clip here will be because the return/send
signal was already clipped, or (and not so believable) the
send output is clipping the return input.
If you are using headphones, use exactly the same approach
as above.
OK, that's one end sorted. Now let's take a look at the other
end; the mixing desk and recording.
Mixing Desk
Essentially the mixing desk will provide two mechanisms
for detecting clipping; firstly through any meters that it may
provide, and secondly through any headphones, monitor
speakers, or output speakers.
Detecting clipping through the headphones or speakers
attached to the mixing desk is exactly the same as discussed
above. Here we will look at using the meters.
With Gain/Faders on the individual channels the aim is
normally to aim for unity gain and then use the master level
to control the output.
My mixing desk only has 1 set of stereo LED meters. These
measure the output level after the master level fader. The
scale is -24, -6,0,+6,Clip. The -24,-6 and 0 LEDs are green,
+6 yellow and Clip are red.
To obtain unity gain the faders are set to unity (0), the
master is also set to unity (0). Then watching the LEDs you
raise the input gain until you have 0dB on the LEDS often,
but no peaks over this. At least this is the usual set-up. My
Peavey RQ200 recommends setting up as before but this
time raising the input gain until clipping just starts to occur,
and then backing off to ensure no clipping takes place.
Clipping as they define it is when the red LEDs light up.
This can be fairly dim if the clip is quick, so a slightly dim
room is a good start here. I suppose the Peavey theory
behind this set-up is by using the loudest signal possible
© Copyright 2000-2002 Barry S. Pearce et al.
Section 9
without clipping, you are getting the best Signal-Noise
ration possible. Fair dinkum.
If you are clipping with all faders at unity and the input gain
at 0 then you might be tempted to back off the channel
fader. If you can, try to avoid this. You might still be
clipping the input that isn't necessarily metered on some
mixing desks. Instead go back up the chain and turn down
whatever is driving the desk.
Well, that's the desk done. Now the only problems that can
occur will be with what the desk is driving. If your PA
speakers are suggesting clipping, start at the far end with the
PA speakers and work backwards as per the speakers above.
The other thing the mixing desk is likely to be driving is
some recording equipment such as a sound card on a PC...
In Sound Forge/Cakewalk:
Problems here are slightly harder to find, due to the length
of the chain involved, but are often easier to see. It is
possible to see a clipping here that lurks way down your
chain, even though you can't hear it, and it hasn't been
indicated anywhere else. Indeed, what I relate to you now is
an actual problem I had. The techniques will be similar for
other PC set-ups and other wave editing/recording software,
such as other version of Cakewalk Pro Audio, Guitar Studio
etc, SONAR, Steinberg Cubase VST, Emagic's Logic
Audio, DigiDesign's ProTools etc etc etc.
Right then, we can assume that the mixing desk has been
set-up correctly as I detailed in the above. So the output
meters are showing around 0dB.
The PC is set up in the Volume Control dialog box to
record from line in on the SB Live. The fader in the dialog
box is the same as when windows was installed—about
85% of the way up. For reference I set line out playback to
mute to avoid any problems with feedback.
OK. I run up Cakewalk. I have two tracks set to record from
the SB Live. Wave Left & Wave Right. I set the record
buttons, and then bring up the mixing desk in cakewalk.
There are now meters showing for the two channels I have
set to record. Playing the guitar now will show me the levels
being received.
Right, I now alter the Master Out fader on the mixing desk
so that the clip indicators in Cakewalk didn't show up. OK. I
set the record off and record some guitar stuff.
I then pulled the wave file up into an editor (in this case
Cakewalk's own). It is in the wave editor (by zooming in
slightly) that you will notice the clip. If you are driving the
card too hard you are likely to get a clip around 95%. But
don't always expect this. It is possible that a unit elsewhere
in the chain is clipping. This will be should be a series of
peaks all being what looks to be 'chopped' at the same level.
Noise Elimination
55
Advertisement
Table of Contents
