35
E
being processed (as a comparison, an electronic calculator may operate internally with a greater number of
decimal places than can be shown on its display). The DSPs in the ULTRA-CURVE PRO operate with a 24-bit
resolution. This is accurate enough to reduce quantiziation noise to levels which are usually below the audible
threshold. However, when using extreme equalizer settings, some quantizing side effects may be detected.
Digital sampling has one further, very disturbing effect: it is very sensitive to signal overload. Take the following
simple example using a sine wave. If an analog signal starts to overload, it results in the amplitude of the signal
reaching a maximum level, and the peaks of the wave starting to get compressed, or flattened. The greater the
proportion of the wave being flattened, the more harmonics, audible as distortion, will be heard. This is a
gradual process, the level of distortion as a percentage of the total signal rising with the increase of the input
signal level.
Quantization Steps
U (Voltage)
-8 -7 -6 -5 -4 -3 -2
Digital Words
1111
1110
1101
1100
1011
1010
1001
1000
0000
t (Time)
0001
0010
0011
0100
0101
0110
0111
Conversation Rate
8
7
6
5
4
3
1 2 3 4 5 6 7 8
-1
-2
-3
-4
-5
-6
-7
-8
Quantization Errors
(Noise)
Continuous
Analog Signal
Fig. 4.3: Transfer diagram for an ideal linear ADC (2's complement representation)
Digital distortion is quite different, as illustrated by this simplified example. If we take the situation where a 4 bit
word has the positive maximum value of 0111, and add to it the smallest possible value of 0001 (in other words,
the smallest increase in amplitude possible), the addition of the two results in 1000 - the value of the negative
maximum. The value is turned on its head, going instantly from positive max to negative max, resulting in the
very noticeable onset of extreme signal distortion.
4.2.1 The AES/EBU and S/PDIF standards
Essentially, two standards exist for the transfer of digital audio data. Their most important electrical specifica-
tions are summarized in Table 4.1. AES/EBU is a professional, balanced connection using XLR connectors.
For semiprofessional users, Sony and Philips have opted against balanced connections and use either cinch
connectors or optical waveguides. The process which was standardized as IEC 958 and is generally known as
S/PDIF (Sony/Philips Digital Interface) became best known for the associated efforts to introduce copy protec-
tion, however.
4. TECHNICAL BACKGROUND
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Summary of Contents for ULTRA-CURVE PRO DSP8024
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