Lexicon
16
Using the 20/20 AD
About Dither
Dither is a low-level pseudo-random signal which is added to digital audio to
reduce quantization noise, in effect, by replacing it with a “nicer sounding” noise.
If the recorder or workstation which follows the 20/20 AD is capable of recording
or processing 20 bits, the DITHER switch should be set to 20 BIT. If, however,
the equipment can only record or process a 16-bit signal, either WIDE or HF
dither should be selected. This is true even if the compressor is on; the dither
generator always sends the appropriate signal for a 16-bit recorder, regardless
of the compressor settings.
All three of these basic dither types have the same quantization noise reducing
effect, but differ in the spectral distribution of the “replacement” noise.
WIDE dither produces white noise.
HF (high frequency) dither produces noise whose amplitude is lower than WIDE
at low frequencies, but higher at high frequencies. Theoretically, this is less
audible than WIDE dither, but just as effective.
20 BIT dither has the same spectrum as HF dither, but with a lower amplitude.
This setting should be used when recording to 20-bit media.
It is possible to filter the quantization noise in such a way that almost all of the
noise within the frequency range where human hearing is most acute is shifted
to higher frequencies. This is called
psychoacoustically optimized noise shaping
(PONS) because it takes advantage of the variations in the ear's sensitivity to
noise within the 20 Hz - 20 kHz range.
To activate this dither, press and hold the ALT button, then press DITHER. The
three dither lights will go on (WIDE, 20BIT and HF) to indicate that you are in
PONS mode. Note that, due to limitations in processing power, the compressor,
4-channel mode and the ALT-MUTE function are disabled while PONS mode is
active. To deactivate PONS, simply press DITHER.
Psychoacoustically
Optimized Noise
Shaping (PONS)
