dbx Pro QUANTUM user manual Appendix B TypeIV White Paper, Converted Level vs. Input Level

Appendix B TypeIV™ White Paper

QUANTUM

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!

Converted

Signal

Level

dB FS

A/D Clip Point

0

-4

					ic
				hm
			rit
		a
	g
o
L

Region

Linear Region

					dB
-4	0	+4	+8	+12	Input
					Signal
					Level

Figure 1 - Converted Level vs. Input Level

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.

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64 QUANTUM User Manual