Setting Up The Processing
29
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
you are free to experiment to get the bass sound you're after.
Additionally, bass tune control allows control of the 'flavour' of the bass by adjusting various points in the bass
dynamic control system.
Xover
The Xover in the DSPX has two selectable frequencies per band split.. The band1/2 split can be set to 150 or
200Hz. The band2/3 split can be set to 720 or 1000Hz and the band 3/4 split can be set to 4000/6000Hz.
Setting the band1/2 split to 150Hz will provide a fatter low end bass sound while 200Hz may provide a more nat-
ural warmer sound. The band3/4 split is probably the most audibly noticable. Setting this split to 4000Hz will lift
up the audio in the presence region which gives the perception of additional loudness. Setting it to 6000Hz will
raise the high frequencies and add a little more sparkle. Some DSPX users have commented that this control
really changes the charachteristics of the processors sound. You can try both and see what suits your format.
We also provide the option of controlling how far band 4 extends to. The options are 15000Hz and 20000Hz. If
you are ONLY processing for FM we suggest you set this to 15000Hz as this will restict super high frequency
energy from entering the AGC and limiter stages which could cause unneccesary control of <15000Hz energy
The xover employs linear phase FIR filtering for audio transparency. Extra delay lines time align the audio bands
ensuring a flat response across the whole audio spectrum regardless of gain reduction levels. Unlike most other
audio processors the DSPX maintains this linear phase time aligned property throughout all of its processing
stages. This can be verified by the application of a low frequency square wave to the DSPX's inputs and moni-
toring the flat top response on the DSPX's outputs. You must make sure that all of the bass enhancement and
input conditioning filters such as the phase rotator are switched to off before conducting this test. The bypass
preset will do this for you (pre-emphasis and de-emphasis is not switched by a preset change).
Multi-band AGC
The multi-band AGC stage of the DSPX is identical to the wideband AGC except for the fact that it operates
on the four band outputs of the Xover. The controls to the multi-band AGC are identical to that of the wideband
AGC. We have also included access to the AGCs ratio controls and this will be touched on in this section. The
other controls won't be discussed further as they are described in full in the wideband AGC section of this chap-
ter.
The Multi-band AGC stage of the DSPX has two main functions.
1. To re-equalise the program material to provide a consistent tonal balance and sonic signature.
2. To prevent excessive limiting by the following peak limiter stages.
Because of the RMS based level detectors the multi-band AGC can re-equalise the sound in a more natural
manner than the peak limiter stages which use peak detectors. As the human ear works on average loudness
rather than peak level the re-equalised audio will sound more natural when dynamic range reduction is per-
formed by RMS based level detectors.
Because the peak to average ratio of the program material can be quite wide it is still necessary to control the
peaks of the audio with the multi-band limiters but unlike most other audio processors the bulk of the work has
been performed by the multi-band AGC and the limiters can be fed with a more controlled level allowing them to
operate in their sweet spot. This is the optimum configuration. Because the multi-band AGC can sometimes do
the job too well we allow the user access to the ratio controls of each band. With these you can determine just
how aggressive you want the multi-band AGCs to be. Some processing fans do like the sound that fast limiting
produces by driving the peak limiters harder and this can be achieved in a number of ways one of which is by
reducing the ratio control to lower settings such as 2:1. This also creates a gentler AGC action.
Please note that lower AGC ratios will equate to less gain reduction. Expect to see much lower gain reduction
figures on the meters. Values around 4-8dB are typical with a ratio of 2:1
Like the wideband AGC the multi-band AGC can be force gated on each of its bands. The force gating allows
us to switch off the AGC for any or all of the bands. By bypassing that bands AGC we allow the audio to pass
through unprocessed to the multi-band limiter.
There are several reasons why you may wish to do this.
1. To let the following limiter have full control of the audio for sonic effect. For example, you may want to create
maximum bass punch, albeit at the risk of distortion caused by overdriving the limiter with certain program mate-
rial. The same applies for HF control.
2. You may want to use the multi-band AGC as a linear phase four band fixed EQ. the gain of each band being
set by the combination of drive and RTR level.
