Yamaha D24 Owner's Manual - Page 188

Digital I/O & Wordlength 189 Digital I/O & Wordlength When a high-resolution digital audio signal is transferred to a lower-resolution system, care must be taken to ensure that the digital audio samples are truncated correctly. When a 24-bit signal is transferred directly to a 16-bit DAT recorder, for example, low-level detail is lost when the eight least-significant bits (LSB) of each audio sample are discarded, resulting in distortion and a grainy sound. The greater the truncation, the greater the distortion. To optimize the truncation process, a technique known as digital dither is applied before feeding the signal to the lower-resolution system. Digital dither works by comparing the output of a special pseudorandom number sequence generator with the lowest data bit of the shortened audio sample and the unwanted bits. The lowest bit is then rounded up or down prior to D/A conversion. Digital dither endows the digital signal with a noise signal (hiss) close to the minimum theoretical limit, which is around -96 dB for a 16-bit signal, although this is considered to be less offensive than the distortion caused by truncating without dither. To minimize the noise, some digital audio processors use noise-shaping techniques to shift it into areas of the audio spectrum where the ear is less sensitive. Unless you have a specific reason for not using it, digital dither should be used when transferring high-resolution signals to lower-resolution systems. In the following system, a 24-bit recording resolution is used for multitrack recording on the D24, and a 16-bit resolution for stereo recording on the DAT. The digital dither function on the digital mixing console is set accordingly. D24 OVER -dB 0 2 6 10 12 14 20 18 30 20 42 26 60 READY 1 2 3 4 5 RECORD READY SOLO/ SELECT PEAK HOLD AUTO INPUT ALL INPUT MONITOR SELECT OVER 0 -dB 2 6 12 20 30 42 60 READY 0 0 0 0 0 0 0 0 ABS H M S F YAMAHA D24 LOCK WC INT FS 48K BIT 24 TC MASTER L R 6 7 8 7 8 9 PROJECT SELECT 4 5 6 LOC MEM RECALL FORMAT CHASE 1 2 3 LOC MEM STORE 0/- CANCEL ENTER LOCATE TIME DISPLAY CAPTURE ABS/REL REMAIN VARI SPEED UTILITY SETUP V. TRACK SELECT EDIT UNDO/ REDO JOG ON DIGITAL MULTITRACK RECORDER PROJECT SEARCH LAST REC IN OUT SET AUTO PUNCH RTN TO ZERO ROLL BACK A B REPEAT REHE AB REW FF STOP PLAY REC JOG/DATA SHUTTLE/ CURSOR POWER ON OFF 0 10 PHONES LEVEL PHONES Recording resolution: 24-bit 02R AES/EBU (24-bit) mYGDAI YGDAI (SLOT 1) DAT 00.00.00.00 DAT Recording resolution: 16-bit S/PDIF (16-bit) Digital input DIGITAL STEREO COAXIAL OUT Slot Output Select SLOT 1: Bus 1-8 Dither setup BUS 1-8: 24-bit Stereo out: 16-bit D24-Owner's Manual