Z-Systems z-qualizer - Manual (Page 4)

z-Qualizer manual Z-Systems Audio Engineering
4
24 un
24 di
20 un
20 di
16 un
16 di
16 p2
16 p3
The last two POW-r dither options are only available at 44.1 or 48 kHz. The sample
rate cannot be altered as the system is always slaved to the incoming rate.
Using the dither and wordlength settings
When the z-Qualizer equalizer is feeding additional digital processors, nearly always
set the output wordlength to 24 dith. This is the maximum wordlength available in
AES/EBU and will send the highest resolution signal to the following device. The
dither in the z-Qualizer is a carefully-randomized floating point dither which removes
quantization distortion. The dither noise level at the 24 dith setting is at approxi-
mately -141 dB below full scale, so we doubt you will consider this to be an audible
problem! (To put this in perspective, most people consider analog tape hiss below
about -80 dB to be inaudible, and the noise floor of the best analog audio console in
the world is around -90 to -100 dB below full scale. Microphone preamplifiers can do
a bit better, but in the real world, noises add, and the practical full band noise of the
quietest typical musical recording is rarely better than about -70 dBFS, excluding
fadeouts).
However, the ear can easily hear signal as much as 20 dB or better below the wide-
band noise level, depending on the frequency and masking. That’s why we have to
use dither noise: to eliminate low level distortion caused by DSP processing. Without
dither noise, the sound of quantization distortion can reduce stereo imaging, and
make the sound cold and harsh, something to be avoided in most cases. The undith-
ered menu choices actually truncate the output of the z-Qualizer without concern for
quantization distortion.
The other dithered wordlength settings are only to be used if the z-Qualizer is con-
nected directly to a following device which truncates the wordlength. For example,
use 20 dith if the z-Qualizer is directly connected to a 20 bit ADAT. Use 16 dith or 16
pwr if the z-Qualizer is connected directly to a 16-bit storage medium such as DAT or
CDR. A router may be used, but no additional DSP processor should be between the
Z Sys and the 16 or 20 bit device.
The only exception to the dither rule: you might choose to select the 24 undithered
option if you wish to bypass the z-Qualizer without turning the left knob to the byp po-
sition (in an automated session, for example, where one tune passes through flat
without any alteration). In this case, select 24 un and make sure that all the gains