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Section 2 Audio Terminology
Audio Terms
Before we get going, I feel that I should explain some
common terms. A good understanding of what these terms
mean, their implications and their relevance to us, will
certainly make the descriptions in the rest of this document
much more meaningful. It is possible that many of you have
come across these terms before. Maybe others haven't so
please bear with me for a little while, while I explain these
terms.
Signal
An audio signal is an analogue or digital representation of
the sound that we hear. The analogue representation is a
voltage. For instance, when your strings vibrate on your
guitar the pickups convert the vibration to a voltage. This
voltage is the audio signal. An Analogue to Digital
Converter (ADC) changes an analogue signal (voltage) into
a digital one. To move the other direction you use a Digital
to Analogue Converter (DAC). Both these may be
integrated into a single chip known as an ADAC.
Mono Signal
A mono signal is a single audio signal. As there is only one
channel, it is not possible to have different sounds for left
and right. To do this you need 2 signals, which leads me
nicely on to...
Stereo Signal
This signal is in fact two mono signals; one for left, and one
for right. It is fairly normal to group the two together and
talk about a single stereo signal. The left and right channels
must differ. If they do not they what you have is '2 Channel
Mono'. Two Channel Mono is often misinterpreted as
Stereo, but this is not so.
Unbalanced Signal
This term is used with regard to wiring. An unbalanced
signal will use a single wire to transmit a signal. Typically,
a guitar outputs an unbalanced signal. The GT-3/5 inputs
and outputs are all unbalanced as well. To change between
unbalanced, balanced and vice versa you need a special
converter, although that said, some equipment have
converters built in.
Balanced Signal
A balanced signal uses two wires to transmit the SAME
audio signal. Do NOT confuse balanced with stereo.
Although two wires are need and the two signals differ a
balanced signal is still MONO. The point of using balanced
signals is primarily one of noise reduction. Typically there
are two signal wires called 'hot' and 'cold' respectively.
The 'hot' signal is our normal unbalanced signal, and the
'cold' signal is the hot one phase inverted. The theory is
that when external noise affects the cable it will affect both
signals equally. So on the 'hot' wire we have +signal+noise
© Copyright 2000-2002 Barry S. Pearce et al.
and on the cold wire we have –signal+noise. When the
signal arrives at its destination the cold signal is inverted
giving us +signal–noise. The two wires have their signal
mixed to return us to a single signal (which is effectively
addition) and this gives us +signal+noise+signal-noise.
Simple maths gives us the answer as 2 x signal and NO
noise!!! Here is a good diagram (courtesy of Behringer
International GmbH) that shows this visually.
Signal Path
The route the audio signal takes through the various cables
and pieces of equipment is know as the signal path.
Signal Level
This is the amplitude of the voltage. It can be measured in
two ways – peak levels and RMS (Root Mean Square)
levels. RMS is a way of taking an oscillating signal (AC
electricity) and resolving it into an equivalent non-
oscillating signal (DC voltage). This is a way of
determining the total power of a signal. Signal-Noise ratios
(explained below) are measured in RMS.
Signal-Noise Ratio
This is sometimes called 'Dynamic Range'. All electronic
and electrical devices generate noise. Signal-Noise Ratio is
basically how much louder the audio signal is, compared
with the noise. Many electronic devices such as stompboxes
and mixers etc are marked with their S/N ratio. Basically
the lower the better—i.e. (quoting from 'Guitar gadgets') A -
60dB S/N ratio means noise you can clearly hear but is
probably not overly objectionable. A ratio of -70dB S/N
means the noise is still there but is considerably less
objectionable. If the S/N ratio is -80dB then the device will
be quiet enough for everyone and at -90dB and greater you
are going to have to really look for the noise.
My mixer comes in at about–97dB, my Alesis RA100 is at -
100dB, the Samson wireless is better than -100dB.—you
get the idea. The GT-3 is -100dB or better., and the GT-5 is
marginally quieter at –105dB or better. (Although not
labelled SNR the GT-3/5 manuals use the term 'Dynamic
Range' to define the SNRs).
However, there are some general principles we can observe
here. Let us say I have a signal of level 100 and this goes
through a device that will generate 10 units of noise. If I
now amplify this signal by 10 then I get 1000 units audio
18
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