WEISS MAN301, Руководство по эксплуатации

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SECTION 3
Some information on the DSD format – properties, caveats,
uses
The DSD (Direct Stream Digital) Audio format is used with the
well-known SACD disc. The SACD has some form of copy protec-
tion implemented, thus an SACD is not easily rip-able into a
computer file.
Quantizing
DSD is a digital signal which uses a 1 bit quantization of the
audio signal at a sampling rate of 64 times the sampling rate of
a Album (64 x 44100 = 2.8224 MHz). The Album format uses a
16 Bit quantization at a 44.1 kHz sampling rate, thus the data
rate of a DSD signal is 4 times the data rate of a Album, which
gives the SACD the potential to represent the audio signal more
precisely.
The noise floor of a signal at 44.1kHz /16 Bit is about 16 x 6 =
96dB below full scale. With the DSD signal the noise floor is 1 x
6dB below full scale, so obviously there have to be taken some
measures to get down the noise floor, else a DSD recording
would be very noisy.
Here the high sampling rate of DSD comes in handy. I.e. with
special filtering techniques (noise-shaping) it is possible to
move the noise in the audio band (0...20kHz) out to higher fre-
quencies above 20kHz. Thus the noise floor in the audio band
can be brought down to very low levels (well below the 16 Bit
noise floor of a Album) at the cost that the noise is at a fairly
high level at frequencies above 20kHz.
Filtering
This high level / high frequency noise has to be suppressed be-
fore the signal hits the amplifier and speakers, in order to avoid
amplifier misbehaving and/or speaker blow-up. A low pass filter
is used to suppress the noise. In a native DSD D/A Converter
this low pass filter has to be implemented in the analog domain
which can be problematic because the non-linear phase charac-
teristics of such a filter. Alternatively this filter can be imple-
mented in the digital domain where the DSD signal is converted
to PCM (at e.g. 176.4 kHz / 24 Bit) and at the same time gets
properly low pass filtered, e.g. with a linear phase filter which is
easily achievable in the digital domain.
DSD uses
The DSD format initially was conceived for distribution and ar-
chiving. Later on it became more and more popular in music re-
cording with its own set of problems as described below. DSD
shows the state of the art of the 90ies. The 1 bit sigma-delta A/
D and D/A converters were very popular at that time. Converter
techniques have progressed though. Today the modern sigma-
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White paper on DSD