dbx IEM, Руководство пользователя

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Appendix B
IEM
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IEM User Manual
analog, we could really exploit its wide dynamic range and more completely capture the essence of the musical perfor-
mance.
Enter the dbx Type IV™ Conversion System. Like its related predecessor technologies—Type I™, Type II™, and
Type III™—dbx Type IV™ succeeds in preserving the wide dynamic range of the original analog signal within a limit-
ed dynamic range medium. Whereas Type I™ and Type II™ expand the dynamic range of analog tape and other limit-
ed dynamic range media, and the simultaneous encode/decode process of Type III™ similarly expands the limited
dynamic range through minimum-delay devices, Type IV™ breaks new ground by greatly enhancing the useable dynam-
ic range of the analog-to-digital conversion process.
The dbx Type IV™ Conversion System combines proprietary analog and digital processing techniques to cap-
ture a much wider dynamic range than the A/D converter could by itself, preserving the maximum amount of informa-
tion from the analog signal. This information is then encoded within the available bits of whichever A/D converter is
used. This means that Type IV™ improves the performance of any A/D converter, from low-cost 16-bit to high-perfor-
mance 24-bit! And no decoding is necessary beyond the conversion process!
As we have previously mentioned, digital systems have a wide linear region compared to analog tape and the
dynamic range of A/D converters has improved significantly in recent years. The dbx Type IV™ Conversion System takes
advantage of this and utilizes the top 4 dB of the A/D converter’s linear dynamic range to create a logarithmic “overload
region.” This allows high-level transient signals passing far above the point where the overload region begins to be ade-
quately represented in just 4 dB of the converter’s dynamic range, whereas a typical A/D converter would clip. With
Type IV™, you can never clip the A/D converter!
Fig. 1 illustrates this concept showing the level of the converted signal below and above the start of the overload region.
The converted signal level is plotted along the Y-axis (vertical axis) of the plot vs. the level of the input signal along the
X-axis (horizontal axis). The logarithmic mapping of the overload region begins 4 dB below 0 dB FS (full-scale) of the
A/D converter. What this shows is that below -4 dB FS, in the linear region, the output signal is the same as the input
signal. Above this, in the logarithmic region, high-level input signals get “mapped” into the top 4 dB of the A/D con-
verter. This mapping is analogous to the signal compression effect that occurs when recording high-level signals onto
analog tape.
Lo
gar
ithmi
c Region
-4
-4
0 +4 +8 +12
dB
dB FS
Input
Signal
Level
Converted
Signal
Level
Linear Region
0
A/D Clip Point
Figure 1 - Converted Level vs. Input Level
TypeIV™ White Paper