dbx 160SWP User Manual
AutoVelocity™ Dynamics
and the dbx 160SL
White Paper
¨
Many audio compressors employ an “Auto”mode to set the attack and release
of the VCA so that the compressor will be well behaved when used in a variety
of situations such as compressing vocals, piano, or program material. “Well
behaved”means that pumping and breathing are minimized and that dynamic
distortion,caused by low frequencies modulating the control line feeding the
VCA,is not audible. The “Auto”mode works beautifully for most compression
needs, however, we often need to compress signals that require a quicker
attack time to catch leading edge transients such as a snare drum hit.
Many compressors on the market have manually adjustable attack and release
controls to give the engineer greater creative control over how the
compressor reacts to a signal. dbx compressors having manual controls
include the 266/266XL,1066,165/165A,the MC6,and new dbx 160S/160SL. If
we look at the markings around the dbx 1066 attack and release controls,we
find the attack range is 3 to .04 dB/msec and the release range is 250 to 5
dB/sec. These markings may seem cryptic at first but, upon further investigation, we find that an attack setting of 3 dB/msec means that the VCA will
reduce its gain at a rate of 3 dB for every millisecond (0.001 second) of time,
or 3000 dB for every second of time. Whereas a release rate of 250 dB/sec
means that the VCA will release its gain reduction at a rate of 250 dB for every
second of time. These attack and release times may seem incredibly fast,but
believe it or not,they are not fast enough for all compression needs. So, why
not just speed up the range of the attack and release controls?
Well,let’s examine the dbx 165/165A. Her attack and release times ranges are
400 to 1 dB/msec and 4000 to 10 dB/sec respectively. Anyone who has used
the 165/165A in the manual attack/release mode knows that it has an
extremely wide range of control and how effective it is for compressing fast
transients by dialing in a fast attack time. However,they also know how easy
it is to get a “bad”sound out of the 165A if the attack and release controls are
AutoVelocityª Dynamics and the dbx 160SL White Paper - November 1998
Page 1
AutoVelocity™ Dynamics and the dbx 160SL
¨
adjusted too fast for a particular application. In fact,most users find that they
use only the upper half (12:00 and clockwise) of both the attack and release
controls for 99% of their compression needs. Inappropriately fast attack and
release times can “chew up”a signal yielding unpleasant results. This is why we
have chosen to limit the range of the attack and release controls on other
compressors we manufacture such as the 1066.
The ultra-fast response of the 165/165A is one reason for its longevity and
“classic” status in the pro audio arena, enabling it to dynamically alter fast
signals as well as provide a creative tool for intentionally shredding the sound,
adding “bite”to vocals,for example. To preserve the heritage of the 165/165A,
we chose to include its manual attack and release characteristics in the new
Blue Series 160S. But in striving to constantly improve our products,we sought
a way to combine the benefits of having ultra-fast response to fast signals with
the forgiving program-dependent characteristics of the Auto mode. Enter
AutoVelocity™ Dynamics processing (AVD). AutoVelocity™ Dynamics
circuitry allows the engineer to set the attack and release controls for relativity
fast settings and not have the dynamic distortion problems associated with
these faster settings.
The AutoVelocity™ Dynamics circuitry allows the compressor to operate in a
manually adjustable program-dependent mode, meaning signals that change
slowly experience slower attack and release times than what are indicated by
the attack and release controls; see Figures 1 and 2. For signals that change
quickly (i.e. snare drum hit), the attack and release response speeds up to
reflect the actual settings of the attack and release controls; see Figures 3 and
4. The faster attack time allows us to catch the transients without allowing
overshoot and to release quickly from the larger change of compression
without “punching holes”in our sound. So, we get to use the full range of the
attack and release controls without being overl y cautious of setting the controls
AutoVelocityª Dynamics and the dbx 160SL White Paper - November 1998
Page 2
¨
AutoVelocity™ Dynamics and the dbx 160SL
Loading...