Digital I/O & Wordlength - Yamaha D24 Owner's Manual

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 com-
paring the output of a special pseudorandom number sequence generator with the low-
est 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 mini-
mize 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 spe-
cific reason for not using it, digital dither should be used when transferring high-reso-
lution 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
TIME DISPLAY
CAPTURE ABS/REL REMAIN
OVER OVER ABS H M S F
–dB 0 0 –dB
2 2
6 6 VARI
UTILITY SETUP
10 12 12 SPEED
14 20 20
18 30 30
20
42 42
LOCK WC INT FS 48K
26 60 60 V. TRACK UNDO/
EDIT
READY READY BIT 24 TC MASTER SELECT REDO
L R
PROJECT
1 2 3 4 5 6 7 8 7 8 9 JOG ON
SELECT
RECORD
READY
4 5 6 LOC MEM
RECALL
SOLO/
SELECT
LOC MEM
1 2 3
STORE
PEAK AUTO ALL FORMAT CHASE
HOLD INPUT INPUT
0/-
CANCEL ENTER LOCATE
MONITOR SELECT
JOG/DATA SHUTTLE/
CURSOR
Recording resolution: 24-bit
DAT
DAT
00.00.00.00
Recording resolution: 16-bit
DIGITAL MULTITRACK RECORDER
POWER
AES/EBU (24-bit)
ON OFF
PROJECT SEARCH LAST REC
AUTO
IN OUT SET
PUNCH
RTN TO ROLL A B REPEAT REHE
ZERO BACK A B
0 10
PHONES
LEVEL
REW FF STOP PLAY REC
mYGDAI
PHONES
S/PDIF (16-bit)
Digital input
Digital I/O & Wordlength
02R
Slot Output Select
SLOT 1: Bus 1–8
YGDAI
(SLOT 1)
Dither setup
BUS 1–8: 24-bit
Stereo out: 16-bit
DIGITAL STEREO
COAXIAL OUT
189
D24—Owner's Manual