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SBM (Super Bit Mapping) Function
During analog recording, the SBM function lowers noise
within the frequency band to which to the human ear is
most receptive to noise, thereby, sharply expanding the
auditory dynamic range of the recorded signal.
To activate the function, turn on the SBM switch when
recording an analog source through the analog (LINE IN)
connectors except when long-play mode (32 kHz) is
selected.
High-precision pulse A/D converter
The DAT deck uses a pulse A/D converter and decimation
filter to convert an analog signal into a quantized 24-bit
digital signal. DAT. like CDs, uses 16-bit quantization, and
thus the 8-bit difference results in more precise
quantization, more signal information and less quantizing
noise than16-bit quantization. During conversion of the 24-
bit data to a 16-bit DAT recording signal, the SBM function
boosts sound quality by reintegrating into the 16-bit signal
4 bits of signal information that would normally be lost.
Applying the principle of human hearing
The SBM function applies the principle of human hearing in
the reintegration of signal information. The auditory range of
the human ear is generally considered to be 20 Hz to 20
kHz; hearing sensitivity, however, shows greater sensitivity
to the range between 3 kHz and 4 kHz, and lower sensitivity
to frequencies above and below this range (see Fig. HN ).
This principle applies also to quantizing noise as well. By
reducing quantizing noise in this particular range, signals
can be recorded to produce more expansive sound than is
possible by a uniform reduction of noise over the entire
audible range.
Se
ee
ee
20
0
100
200
oom
a
10
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Sampling frequency (Hz)
18
Noise-shaping filter
The SBM function uses a noise-shaping filter (see Fig [E])
with a frequency response similar to that of the human ear
to reduce quantizing noise within the most sensitive
frequency range. and to feed back the quantizing error
(that is normally lost) back to the input signal. re-integrating
the low-end bit information with the high-end bit information
(see Fig. Ei ).
Quantzer
16-bit
SBM
output
24-bit information
Norse-shaping filter
a) Coetticrent
Fig.
shows the improvement in the quantizing noise level
when the SBM switch is on. Given a noise level of 0 dB
when the SBM switch is off. the improvement in noise level
for sampling frequencies lower than 3 kHz exceeds 10 dB
when the SBM Is activated
Nose {1 TT
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100
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1m
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Sampling trequency (Hz)
The SBM function operates only during recording The
improved sound produced by the SBM function. however,
can be enjoyed during playback, regardiess of the SBM
switch position or the DAT deck being used
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