212 Chapter 16—Using the Digital Inputs & Outputs
Output Dither
When a high-resolution digital audio signal is transferred to a lower-resolution system, some of the least-significant bits (LSB) of data are ignored by the receiving system, which can make low-level signals sound grainy and step like, similar to the noise produced by a low-resolution digital reverb as signals fade. To prevent this, the wordlength of a digital audio signal can be shortened to match that of the receiving system. Instead of simply chopping the unwanted bits off, the 01V uses the industry-standard technique known as dither is used to optimize the wordlength reduction process.
Dither can be set independently for the Digital Stereo Out and Option I/O digital out- puts, and should be matched to the wordlength supported by the receiving digital audio device. For example, with a 16-bit DAT recorder connected to the Digital Stereo Out, the DIGITAL ST OUT should be set to a wordlength of 16, and with a 20-bit digital multitrack recorder connected via the Option I/O, OPTION OUT should be set to 20.
1. Use the [SETUP] button to locate SETUP page 5, as shown below.
2.Use the cursor buttons to select the WORD LENGTH switches, and the [ENTER] button to set them.
Dither works by comparing the output of a special pseudorandom number sequence generator with the lowest data bit of the shortened data word and the unwanted data bits. The lowest bit is then rounded up or down prior to D/A conversion, thereby opti- mizing the digital output signal for use with lower-resolution systems. Since dither endows the digital signal with a noise floor close to the minimum theoretical limit, some audio professionals choose not to use it for applications with a wide dynamic range, such as classical recording. If you’re in any doubt, it’s probably best to use it.
