Lexicon 20/20 AD manual About Dither, Psychoacoustically Optimized Noise Shaping Pons

Using the 20/20 AD Lexicon

About Dither

Psychoacoustically

Optimized Noise

Shaping (PONS)

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.

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