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Crosstalk
Commonly in audio systems:
Crosstalk is referring to signal leakage
from one circuit to another, or between
cables, and is always present to some
extent in any sound system.
What causes Crosstalk in audio systems…
What causes Crosstalk in audio systems…
Crosstalk can be caused by inductive or
capacitive
coupling
between
separate
circuits,
It can be aggravated by:
1. Poor circuit design
2. Improper physical component layout
within equipment
3. Improper cabling techniques
Crosstalk : unwanted leakage or bleed of a signal from one or more
channels to other channels within a device or cables
Inductive coupling:
Is the phenomenon in which the change in current through one wire
or a circuit induces a voltage across the ends of the other wire or
circuit through electromagnetic induction.
Inductive coupling:
Is the phenomenon in which the change in current through one wire
or a circuit induces a voltage across the ends of the other wire or
circuit through electromagnetic induction.
In Systems
In Cables
Capacitive coupling :
Capacitive coupling is the transfer of energy within an
electrical network by means of the capacitance between
circuit nodes.
This coupling can have an intentional or accidental
cause. Capacitive coupling is typically achieved by placing
a capacitor in series with the signal to be coupled
Capacitive coupling :
In Systems
In Cables
When two cables, particularly long cables
as from a stage to a mixing console in the
back of the house, are bundled in close
proximity, there is a lot of area exposed
whereby capacitive and/or inductive
coupling of signals can occur.
So-called snakes or multi-core cables are
the most susceptible to such coupling.
Measuring crosstalk
We stimulate Channel 1 with a signal, but measure the output of Channel 2.
Channel 2 has no input, so on a device with zero crosstalk; it would have no
output signal.
Where crosstalk is present, we’ll see some signal that corresponds with the
signal we are giving in Channel 1.
To get a value for crosstalk, we take the RMS voltage level from the channel
we are measuring (channel 2) and divide by the RMS voltage level we
measure on the stimulated channel (channel 1).
Because Crosstalk is a ratio, it’s usually expressed in dB.
Measuring crosstalk
Device under test
Unfortunately,
the situation is seldom
that simple.
Crosstalk values will change with frequency.
If the crosstalk is caused by inductive coupling,
it will be greater at low frequencies. If caused
by capacitive coupling, it will be greater at
high frequencies.
The frequency at which the crosstalk is measured
is thus important.
Some manufacturers will provide this specification,
as follows:
Crosstalk (Adjacent Channels):
Equal to or better than -60 dB
below 1 kHz; -50 dB at 10 kHz
An even more useful crosstalk specification is provided by
graphing the crosstalk between channels, as shown below:
Where to measure crosstalk?
Crosstalk always is present in controls, switches, faders, etc.
Crosstalk can be measured across almost any circuit paths, and it will
always have some impact on performance - it is not unlike distortion,
even at low levels, so it is to be avoided.
While there are dozens of circuits across which we can measure
crosstalk, we can't expect all this information in a regular spec of a
device.
It does take up a lot of space to list all these data, however, some
responsible manufacturers present the most critical information
analytically.