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Digital I/O & Wordlength 189
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.
Recording resolution: 24-bit
Recording resolution: 16-bit
00000000
YAMAHA D24
OVER
READY
0
2
6
1012
1420
1830
20
42
2660
–dB
OVER
ABS H
LOCK
TIME DISPLAY
CAPTUREABS/REL
REMAIN
VARI
SPEED
UTILITY
SETUP
PROJECT
SELECT
LOC MEM
RECALL
LOC MEM
STORE
LOCATEENTERCANCEL
0/-
1
4
7
8
R
7654321
RECORD
READY
SOLO/
SELECT
MONITOR SELECT
PEAK
HOLD
AUTO
INPUT
ALL
INPUT
FORMATCHASE
L
2
5
8
3
6
9
UNDO/
REDO
EDIT
JOG ON
JOG/DATASHUTTLE/
CURSOR
PROJECT SEARCH
RTN TO
ZERO
REW FF
STOP PLAY REC
ROLL
BACK
LAST REC
SET
DIGITAL MULTITRACK RECORDER
REPEAT
REHE
PHONES
LEVEL
010
ON
POWER
OFF
PHONES
BA
B
A
AUTO
PUNCH
IN
OUT
INT
24
48K
MASTER
WC
BIT
FS
TC
MSF
READY
0
2
6
12
20
30
42
60
–dB
V. TR A C K
SELECT
mYGDAI YGDAI
(SLOT 1)
AES/EBU (24-bit)
S/PDIF (16-bit)
D24
DAT
00.00.00.00
DIGITAL STEREO
COAXIAL OUT
Digital input
DAT
02R
Slot Output Select
SLOT 1: Bus 1–8
Dither setup
BUS 1–8: 24-bit
Stereo out: 16-bit