Input Signal Compressor/Limiter; Peak Voltage Limiter; Average Power Limiter; Clip Eliminator - Crown I-T4000 Operation Manual

4 Advanced Operation

4.6.14 Input Signal Compressor/Limiter

An input signal compressor/limiter is available for each channel. Five
parameters control this feature:
Enable: Enables or disables this function.
Threshold: Sets the level, in dBu, above which the compressor
begins to attenuate the input signal. This level corresponds to the
input level meter reading. The compressor is "feed-forward," meaning
that the level detection point is located before the gain control stage.
The range is from +20 dBu to – 50 dBu.
Hysteresis: A "dead zone" that ensures a significant change before
acting. The range is from 0 to 12 dB. It requires the signal to go above
the upper threshold before engaging and to go below the lower thresh-
old before releasing.
Attack Time: Sets the attack time of the compressor. The attack time
is defined as the time it takes the compressor to attenuate the signal
gain by 20 dB. The range is from 1 millisecond to 0.1 second.
Release Time: Sets the release time of the compressor. The release
time is defined as the time it takes the compressor to increase the sig-
nal gain by 20 dB. The range is from 10 milliseconds to 10 seconds.
Compression Ratio: Sets the compression ratio of the compressor.
The ratio is the relation between the amount of attenuation applied by
the compressor verses the amount that the input signal is over the
threshold. The available settings are 2:1 to 32:1.
Beyond the three controls for each channel, a single-control Com-
pressor Tie connects the compressors together. The compressors
are tied at their sense points, meaning that the greater of the two input
signals will be used as stimulus for both compressors. Each compres-
sor will still compress based on its individual threshold, attack, release
and ratio settings.

4.6.15 Peak Voltage Limiter

This limits the peak voltage output of the amplifier. Four parameters
control this limiter for each channel:
Enable: Enables or disables this function.
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Threshold: Sets the level, in absolute voltage, which the limiter will
allow from the amplifier. The range is from 12 V to 255 V
pk
Attack Time: Sets the attack time of the limiter. The attack time is
defined as the time it takes the limiter to attenuate the output signal by
20 dB. The range is from 1 millisecond to 100 milliseconds.
Release Time: Sets the release time of the compressor. The release
time is defined as the time it takes the limiter to increase the output
signal by 20 dB. The range is from 10 milliseconds to 10 seconds.

4.6.16 Average Power Limiter

This limits the long-term output power of the amplifier. Four parame-
ters control this limiter for each channel:
Enable: Enables or disables this limiter.
Threshold: Sets the average power level, in watts, which the limiter
will allow from the amplifier channel. The range is from 10 watts to
10,000 watts. This level should be set to the connected loudspeaker's
long-term power rating. Also you must enter the loudspeaker's nomi-
nal impedance.
Attack Time: Sets the attack time of the limiter. The attack time is
defined as the time it takes the limiter to attenuate the output signal by
20 dB. The range is from 1 second to 30 seconds.
Release Time: Sets the release time of the compressor. The release
time is defined as the time it takes the limiter to increase the output
signal by 20 dB. The range is from 1 second to 30 seconds.

4.6.17 Clip Eliminator

This limiter monitors the clip events and attenuates the input signal to
prevent amplifier clipping. The attack and release times are preset to
optimum rates. Only one parameter controls this limiter. "Enable"
enables or disables this limiter.

4.6.18 Limiter Tie

This control forces both channels to track by using the greatest (worst
case) attenuation of any limiter from either channel. With this option
disabled, each channel will independently take the greatest attenuation
of its own four limiters (voltage, power, clip, thermal) and ignore the
limiting of the other channel. Note that this function does not include
the effects of the input compressors. To tie the input compressors, use
the Compressor Tie function.

4.6.19 Load Supervision

The load supervision feature allows real-time monitoring of the load
pk.
connected to each amplifier channel. When enabled, the I-Tech contin-
uously monitors the amplifier output voltage and current, and calcu-
lates the long-term average load impedance. The measured load
impedance is compared against the user-defined high and low limits.
If either limit is exceeded, the status indicator and, if enabled, the
IQwic Error Reporting functions alert the user of the problem. There are
six controls and two indicators for each channel:
Enable: Enables or disables the load-supervision function.
High Limit: Sets the upper bound above which the system will report
a "high" error status.
Low Limit: Sets the lower bound below which the system will report
a "low" error status.
Nominal Load Impedance: Sets the expected average impedance
for the connected load. This value determines the output signal level
required for the test. This parameter is also used by the average power
limiter to determine the expected power threshold. (See Section
4.6.16).
Report Error to Network: Enables Error Reporting to send an error
report via the network so that high and low load conditions are
reported to the IQ software.
Test Indicator: This indicator is active when the amplifier output sig-
nal is sufficient to allow load impedance calculation and test verifica-
tion.
Low/Normal/High Indicator: This indicator shows the present sta-
tus of the load impedance with respect to the user-defined high and
low limits.
Z Average Monitor: Reports the actual calculated average load
impedance in ohms. Its range is from 0 ohms to 250 ohms.

4.6.20 Memory Backup Configuration

In normal operation, the I-Tech amplifier stores all its settings in non-
volatile memory. When the power is removed from the amplifier and
then restored, the amplifier uses these backed-up settings for its func-
tions. This feature can be disabled with the memory backup enable
I-Tech Series Power Amplifiers
Operation Manual