Tcm™ Transient Capture Mode; Linked Setups Vs. Mono Setups; Dithering - dbx DDP Manual De Operador

Section 6: Appendices
TCM™ -- Transient Capture Mode
Transient Capture Mode™, or TCM™ works on the principle of delaying the audio signal up to 30µs, and letting
an unheard "control" signal begin to activate the response of the VCA. The overall result is the perception of a
very fast moving compressor, able to catch the front of almost any transient signal, but not delaying the audio sig-
nal enough to produce any phase correlation errors. In the DDP, you may vary the delay, in the form of a TCM
delay control, with a range from 0µs (microseconds (µs) are measurement units in 1000ths of a second) to 3ms.
While this is not enough delay to cause phasing errors, it is enough to give the device time to start to react before
the signal arrives at the point of processing.
The controls for the TCM section are in the Gate parameter area, but its effect is global.
The resulting TCM implementation in the DDP allows you to vary the amount of delay, based on the transient
characteristics of the signal being processed. The signal sounds smoother and easier for the DDP to process in the
compressor, limiter, and de-esser functions.

Linked Setups vs. Mono Setups

As you become more familiar with the DDP, you may want to begin creating your own custom setups. Doing so
requires that you build your own setup from the "framework" of another setup. In other words you use a factory
setup to begin to create your own setup. The factory setups are grouped into two groups: Linked setups vs. Mono
setups. In order for you to creat a linked setup, you must choose one of the linked factory setups as your starting
point. If you want to build two mono setups you must start with a mono setup as your starting point. It is import-
nat to realize that LINKED SETUPS CANNOT BE UNLINKED, and likewise, UNLINKED SETUPS CANNOT BE
LINKED. If you wish to create a linked setup, you MUST start with a linked setup, and if you want to create a
mono setup, you MUST start with a mono setup.

Dithering

In analog recording, the noise floor is not correlated to the input signal. Tape hiss sounds the same if you are
recording a drum or a guitar or vocal. This characteristic is called uncorrelated. One of the real limitations of
digital recording is that the noise floor is not smooth and in fact changes with the signal. This is called correla-
tion. A correlated noise floor will often modulate up and down with a low level signal input. This modulation is
only apparent when reducing the number of bits used to capture the signal. If you are using the DDP analog
outputs, the 24 bit D/A utilizes the full range of the 24 bit DDP signal path. However, if you are recording from
the digital output of the DDP to something like a DAT player which only has 16 bit resolution, then you should
use dither.
Dither is used to "smooth out" the digital noise floor, giving it an analog-like characteristic. Dither is actually a
low-level random noise added to the signal before it is truncated to the smaller bit width. The resultant noise
floor will be uncorrelated with the input signal, so it will not modulate with the signal. Because you are adding
noise, you will hear the noise floor of the output signal raise slightly, but it will not have the harshness that is
often associated with digital recording. Numerous psychoacoustic studies have been performed which show that
people prefer the higher level uncorrelated noise floor of a dithered signal to the sound of a truncated correlated
signal. On the DDP you can use flat TPDF dither when mixing to a DAT player. More about TPDF dither can be
found in the paper by Vanderkooy and Lipshitz "Resolution Below the Least Significant Bit in Digital Audio
Systems with Dither", JAES 32:3 1984.
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