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AM-10HD / Aug 2008
F E A T U R E S A N D P R E S E T S
Clean and Loud
To accomplish Clean and Loud we can use the behavior of the ear and brain
(psychoacoustics) to fool it into thinking the station is louder. The following tweaks,
together or in combination, can be used to create a sound that’s loud and punchy, but
also still subjectively clean:
‑ Use slower attack times in the AGC sections
‑ Use slower release times in the AGC sections
‑ Use slower attack times in the 10‑band limiters
‑ Leave the 10‑band release times fairly fast (<100ms)
‑ Increase the drive to the final clipper (not too much!)
‑ Increase the drive to the composite processor and use the Mask Filter
‑ Use a fairly low AGC Low to Mid Low crossover frequency – perhaps around
100‑120Hz
‑ Use a fairly high Mid High to High band crossover – perhaps 3.5 or 4.5kHz
‑ Be gentle with any mid‑frequency equalization. In fact, partially subduing the
range (no more than 1dB to 1.5dB) between about 600Hz and 1.0kHz can sub‑
jectively clean up otherwise harsh‑sounding material. To do this, use the para‑
metric equalizer configured for post AGC/Compressor operation with a center
frequency of around 800Hz, a bandwidth of about 1.0 octaves, and a cut of no
more than about 1 to 2 dB.
‑ Another trick is to use a small amount of fairly narrow EQ cut at 200 Hz. This
will open up the sound on car radios, which typically have a bit of muddy sound
in this region. Use the parametric equalizer either pre or post AGC and set it for:
EQ Frequency of 200Hz
EQ cut of about ‑3dB
EQ Bandwidth of about 0.2 octaves.
The above combination will somewhat “relax” the sound because the AGC sections
are operating slower, slightly lowering their average output levels, and also because
of the slightly reduced levels in the ear’s most sensitive region due to the midrange
equalization. If the “car radio” EQ is used the sound can be significantly opened up
on such receivers while not losing too much in the way of loudness.
You’ll note in the above recommendations that the drive has been increased to the
clippers. The increased clipping depth, albeit only momentary because of the longer
AGC attack times we recommended, will increase the subjective loudness on larger
signal peaks. This will restore a sense of loudness and punch and create a feeling of
dynamics and loudness, and do it without generating the same kind of distortion and
other artifacts that dense compression and higher duty cycle clipping would create.
With the crossover frequencies at the ends of the audio spectrum carefully tuned
to the extremes (within reason of course!), the dynamic behavior of the AGC/Com‑
pressor can create that familiar “smile curve” equalization and lend an overall sense
of Hi‑Fi to the sound without having to rely on using static equalization. In AM what
we’ve done is keep the middle three bands fairly narrow, with the bottom and top
bands tuned to handle the extensions of the audio spectrum. This concentrates the
