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Section 26
The issue of signal delay and signal polarity were raised on
the GT-3 Yahoo Group by Sutton Reid. In this section we
will examine what they are, and I shall present the results
from some tests that were performed to determine the GT-
3/5's affect on the signal.
Both signal delay and polarity were measured using the
following set-up:
PC Line Out
Channel 6.
Channel 6 Monitor Out
right
Channel 5 Send Effects
GT-3 Out (or Send effects)
hard left
Signal Delay
Signal delay is the term used to describe the time it takes a
signal to travel between two points. Almost all audio
processors incur some sort of delay in their circuits, which
is inherent in their design and in the nature of what they do.
Indeed, sometimes this delay is exploited and is mixed back
with the original signal to produce effects such as delay,
chorus and reverb. We however, will be examining what
delay is incurred by the GT-3/5, without any time delay
effects being used. This is the raw delay inherent in the unit.
When performing the tests for signal delay I have checked
the delay on a straight cable, without the GT-3/5, and this
shows a 0.000ms delay. The test set-up is therefore *not* an
affecting factor in any of these tests.
GT-3/5 State
Signal Travel
Distance
Bypass Mode
Input
No Bypass,
Input
No Effects
External
Effects
Input
Loop
External
Effects
Input
Loop in loopback
RETURN
OUTPUT
Preamp
Input
Simulation
OD/DS
Input
Preamp + OD/DS
Input
As you can see, adding more effects results in increased
delay times. The OD/DS is not surprising in its leap in
delay, due to the fact it is an analogue distortion circuit, and
therefore it must pass through the ADAC process. Again
you can see the cost of the ADAC process when the effects
loop is used with a small straight patch cable directly
connecting the SEND to the RETURN.
© Copyright 2000-2002 Barry S. Pearce et al.
Signal Delay & Polarity
Peavey RQ200 Mixing desk
Channel 5 panned hard
GT-3 In.
Channel 4 panned
Delay Incurred
Output
1.088ms
Output
1.383ms
SEND
1.156ms
SEND
2.471ms
Output
1.474ms
Output
2.177ms
Output
2.313ms
Although these times were measured on a GT-3, it is
expected that the GT-5 is identical.
So why are these times important to you? Well, if you use
the GT-3/5 in a parallel effects system you may get different
delays times causes a slight out-of-phase situation and thus
some frequency cancellation, often leading to a thinner
sound. If you read section 29, which describes the external
effects loop being used as a tap, then you can experience
different timings between the main output signal and the
SEND jack signal. Again this can lead to phase
cancellation, and a thinning of the sound.
Signal Polarity
The term signal polarity (also called 'signal phase') refers to
whether an effect is 'non-inverting' or 'inverting'. A 'non-
inverting' effect produces a positive-going output signal
from a positive-going input signal. However, an 'inverting'
effect produces a negative-going output signal from a
positive-going input signal. Problems with polarity only
occur when using parallel effects systems, where a mix of
inverting and non-inverting effects can produce a partial or
complete cancelling of the signal.
The direct signal and the output signal show the same signal
polarity. The mixing desk is neutral as well and does not
invert the phase.
Therefore I must conclude the GT-3 and GT-5 do not phase
invert, and are neutral with regard to signal polarity.
So why is phase inversion an issue? Well if you apply a
phase inverted signal to a normal one, the result is phase
cancellation and either a thinning, or if the signals are
exactly the same, a disappearing of the signal all together!
This obviously will only concern people using parallel
effects systems or are mixing the wet GT-3/5 output with a
dry signal as well.
111
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