360 Systems DigiCart/E - Manual (Page 52)

42 • • • • Recording
DigiCart/E normally records audio using a digital word size of 24-bits. However, it is sometimes desirable
to play out using a smaller digital output word size for use by external equipment, such as a 16-bit DAT
recorder. If the output material is anything but white noise, its sample stream will be correlated. This is
particularly true of music. The effect of simply truncating the 24-bit samples to 16-bits results in the
quantization error being correlated to the signal, producing signal distortion.
Dithering is a technique of adding an appropriate random noise source to the 24-bit digital output stream
before reducing the word size. This effectively decorrelates the quantization error from the signal, resulting
in a very low-level broadband hiss being added to the signal, rather than the more objectionable signal
distortion.
DigiCart/E uses a zero-mean random noise source with a triangular probability distribution. Its peak level
corresponds to the magnitude of the least significant bit of the reduced word size within the 24-bit field.
The method is called “LSB TPDF dither” for Least Significant Bit Triangular Probability Density Function.
The OUTPUT WORD SIZE selection in the Setup menu gives you two choices: 24-BITS (no dithering), or
16-BITS (8-bit dithering.)
The following tables list record and play format options, menu settings, and front panel indicators:
Record Modes
Input Data
Format
Recorded
Format Setup Menu
Format
Indicator
Dithered
Indicator
24 24 SETUP | Record Data Format = 24-Bit 24 OFF
24 16 SETUP | Record Data Format = 16-Bit Dithered 16 ON
16 24 SETUP | Record Data Format = 24-Bit 24 OFF
16 16 SETUP | Record Data Format = 16-Bit 16 OFF
The RECORD DATA FORMAT parameter in the Setup menu specifies both the sample size (16 or 24 bits)
and the file format (DigiCart, WAV, or compressed as AC-2) to be used for recordings.
The RECORD DITHERING setup parameter is used to tell the machine that 24-bit digital data is being
supplied to the digital inputs with the intention of making a 16-bit recording. If the RECORD DATA
FORMAT parameter is set to 16-BIT, then the 24-bit incoming audio is dithered down to 16-bits during the
recording, illuminating the Dithered indicator on the front panel.
Play Modes
Recorded
Data
Format
Output
Data
Format Setup Menu
Format
Indicator
Dithered
Indicator
24 24 SETUP | Play Word Size = 24-Bit 24 OFF
24 16 SETUP | Play Word Size = 16-Bit 16 ON
16 16 SETUP | Play Word Size = 16-Bit 16 OFF
The PLAY WORD SIZE parameter in the Setup menu specifies the sample size (16 or 24-bits) at the digital
output connectors. If the selection is set to 16-BIT and a 24-bit cut is being played, then the sample size is
dithered down to 16-bits, illuminating the Dithered indicator on the front panel.