Specifications

Setting Up The Processing
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The coupling control controls the amount of audio that is fed from one bands detector into the neighbouring
bands detector. The audio is fed from one bands detector through the coupling ratio control and then the highest
level wins.
For example, if we coupled band 2 to band 1 with a coupling of 50% we would ensure that the band 1 gain
reduction could never decrease (less gain reduction) more than 6dB past the band 2 gain reduction. If the cou-
pling was set to 100% then the band 1 gain reduction would follow the band 2 gain reduction when the band 1
gain reduction would have been less than the band 2 gain reduction. Setting the coupling ratio to 0% would let
both bands operate independently of each other.
We can limit the amount of low and high frequency re-equalisation by carefully setting the B1<2 and B4<3 cou-
pling controls. If lighter processing is desired it is common to link the bands to a certain amount, where pop and
CHR formats usually desire low or uncoupled ratios. Coupling ratios around 30% are usually a good compro-
mise to maintain cut-to-cut consistency through multi-band re-equalisation while maintaining most of the original
spectral balance of the source material.
Band-to-Band Coupling
The low frequency band (B1) can be restricted from ever adding more gain than is user-specified, with respect
to the dynamic gain of the low mid band (B2), using the “B1<B2” menu setting. Likewise, using the “B3>B4”
menu setting, the high frequency band (B4) can be restricted from adding more gain than is user-specified, with
respect to the dynamic gain of the high mid (B3) band. When enabled, the restriction controls make it impos-
sible for the Low and High bands to ever operate with more than a specified amount of gain beyond that of the
adjacent band (note: they are always free to operate with less gain). The restrictions are one-way, setting a rela-
tive limit on how much gain can be added in the extreme bands (B1, B4), all the while the dynamic gain controls
in the adjacent bands (B2, B3) are unaffected. A good example to explain the need and setup of such controls
would be if a radio station regularly makes remote broadcasts near heavy traffic, which typically has an excess
of very low frequencies. With the B1<B2 restriction turned off, the low band (B1) is free to bring up the level of
any rumble that may occur above the gate threshold and could potentially be increased nearly to the level of the
other audio. This is a very unnatural-sounding and potentially problematic situation. By setting the B1<B2 cou-
pling to, for instance, 4 dB, the gain in the low band (B1) will can only go as high as 4 dB greater than the gain
occurring in the low mid band (B2), but no more. As long as this condition continues, the B1 gain will track the
dynamic gain of B2, plus 4 dB, but no greater. And having 4 dB more B1 gain than in the B2 band will not sound
nearly so noticeable as 15 to 20 dB more gain! The settings for the B1<B2 and B3>B4 band gain restrictions
can be set to ‘Off’ or to allow anywhere from 15 dB to full coupling (‘0 dB’).
Channel coupling
The control allows you to gang the left and right channel gain controls by a percentage set by the control. If set
to 0dB, the coupling works on a highest level wins basis where the channel with the maximum gain reduction
controls the gain reduction of both channels. This preserves the stereo balance of the original source material.
The control can be adjusted all the way down to OFF at which point the two DSPXtreme multiband AGCs oper-
ate fully independently. This is often known as a dual-mono architecture.
While we would prefer you to buy two processors you could use a single DSPXtreme as two processors,
processing two mono audio feeds. You would need to bear in mind if running the DSPXtreme this way that the
front panel gain reduction metering may not behave as expected because the displayed gain reduction value for
that processing block is the highest gain reduction of the left and right channels.
Bass enhancement
The frequency contouring effect of multi-band audio processors often leaves the bass lacking a little. The sum-
mation of the bands tends to give a boost to the presence frequencies and leaves the bass sounding a little thin.
This effect can be compensated somewhat by enhancing the bass prior to multi-band processing.
The DSPXtreme has two types of bass enhancement filter. A low frequency shelving boost filter and a peaking
bass equaliser.
The shelving filter has a 12dB/octave slope and can be adjusted to provide between 0 and 12dB of bass boost.
Use this control with caution as too much low frequency boost can cause loss of mid-bass because the low
bass, often inaudible on many receivers dominates the gain reduction of the BAND 1 AGC and limiter. A setting
of 6dB is a good compromise and starting point.
The peaking bass equalizer is a pseudo parametric style bass equalizer control that allows you to sweet tune
the bass. Four frequencies, amplitudes and Q's are provided giving you 64 different bass curves to select from.
Frequencies selectable: 60Hz, 76Hz, 95Hz and 120Hz. Q's selectable: 0.4, 1, 2 and 4. Gains selectable: 0,
1.5dB, 3dB, 4.5dB, 6dB. A starting setting of 95Hz, Q of 1 and gain of 4.5dB warms the bass up quite nicely but