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AM-10HD / Aug 2008
A M - 1 0 H D G U I
If for some reason “less” AGC control signal is desired, it may be achieved by
lengthening the AGC attack time.
The Backoff control also affects the degree of coupling between the AGC sec‑
tions of the sum and difference processors. As the Backoff control is adjusted to
more negative numbers the AGC threshold is raised above that of the compressors.
This causes the compressors on both the sum and difference channels to do more
“work,” which increases the obviousness of processing for both signals.
Crossover Frequencies
The AGC/Compressor is a five band design utilizing 48dB/octave phase aligned
filters. Very careful filter and phase equalizer design eliminates unnatural spectral
coloration when deep gain reduction is occurring in one or a few bands.
There are four crossover frequencies to select.
The Super Low to Low band crossover frequency is selected using the red
list box. Frequencies between 40.5Hz and 120Hz may be selected.
The Low to Low Mid crossover frequency is selected using the yellow list
box. Frequencies between 149Hz and 334Hz may be selected.
The Low Mid to High Mid crossover frequency is selected using the green
list box. Frequencies between 817Hz and 1.59kHz may be selected.
The High Mid to High band crossover frequency is selected using the blue
list box. Frequencies between 2.52kHz and 5.99kHz may be selected.
Selecting Crossover Frequencies
The selection of crossover frequencies plays an important role in determin‑
ing how an audio processor sounds with different types of program material, and
therefore the crossover frequencies should be selected empirically but carefully.
The upper and lower range of crossover frequency settings has been calibrated
so that they are most useful with typical program material. In our Factory presets
we have set the Band 4 to Band 5 crossover so that it is appropriate for the AM
bandwidth that the preset may be associated with. In fact, in all Factory presets
we’ve adjusted the crossover so that Bands 2, 3, and 4 are doing a lot of work
in the mid frequencies ‑ these are the frequencies where the most help is needed
in order to maintain good intelligibility with the widest variety of AM receivers.
The bands at the outer frequency extremes, Band 1 and Band 5, handle the
remainder of the audio spectrum. Band 1 handles frequencies between the high
pass filter setting and the Band 1 to Band 2 crossover frequency, while Band 5
handles frequencies between the Band 4 to Band 5 crossover frequency and the
cutoff frequency of the low pass filter as set in the AM TX menu.
