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Frequency Response

Peeking inside these wonder boxes proved enlightening. A single workhorse chip, the Crystal CS492604 handles both Dolby and DTS decoding functions, which drastically reduces the cost. Next, the up to six outputs are managed by the nearly ubiquitous JRC 4558 dual op-amps. While these aren't really audiophile quality (a slew rate of 1V/uS), they provide a top notch cost vs. performance ratio. Realistically, I would have much preferred something of the LM353 op-amp class (13V/uS) and possibly a higher end model might appear (here's to hoping) with theater grade components if these two make as big a market splash as they should.

All interior components contribute to the overall quality however; the frequency response is most affected by the decoding chip and the op-amps.

Frequency Response
Freq (Hz)
29
41
83
100
129
147
196
200
1K
10K
19K
L/R
N/A
N/A
-6
-4.8
-3
-2
-1.1
-1
0
-1
-3
Sub
-3
-1
-.5
0
-.6
-1
-3
N/A
N/A
N/A
N/A

The table indicates a fairly flat composite curve with its -3dB points at 29Hz and 19Khz, which is sufficient for most computer and typical home installations. Note that the bottom curve is from the subwoofer output and not the front L/R outputs. A dedicated subwoofer must be used when listening to all 5.1 channels in order to obtain the lowest frequencies.

Volume Linearity

Linearity has always been of much concern with digital controls. If I want a 30dB reduction in loudness and the meter flashes a number that says so, do I get what was requested? Or, do I get something else? In the early days of digital decoding and digital volume controls, linearity, or the accuracy of the relative output of the audio signal came under fire. I'm happy to report that even in cost effective solutions, reasonable precision has become the defacto standard.

Linearity
Display
+10
0
-10
-20
-30
-40
-50
-60
-69
Actual
+10
0
-9.8
-19.7
-29.7
-39.7
-49.3
-56.7
-60.7

With less than 1dB of error, the volume tracks cleanly over a 60dB (1000:1 voltage wise) region. Distortion and digital "clicking", normally experienced in portable CD players when adjusting the volume controls quickly, did not rear its head to any appreciable degree. Some compression did occur, but only at the lowest levels which practically speaking are lower than 70dB (from +10 to -60) and to be considered as effectively muting the entire output. When the display reads -69dB, it actually measured a very compressed -60.7dB.

Maximum Input & Output Levels

Similar to the ROCCO 5.1's input woes, the highest analog input voltage to the DE series decoders was a far too low 370mV/ch. While most computer sound cards can't exceed this (an SBLive! can), most CD and HiFi VHS players can with ease. Many HiFi units are set up so that 0dB equals 316mV. This means that when loud, +10dB passages occur, the machine is pushing out 1.0 Volts, which will significantly distort the input of the decoder. Because the input is distorted, no adjusting of the digital volume control will eliminate the tremendously distorted output. This means that only very low output analog or pure digital sources can be used.

The final measurement I endeavored to take was the maximum undistorted output level. I was pleasantly surprised when 1.13 Volts displayed on my test gear before the onset of clipping (3%). The DE decoders should have little trouble driving most external amplifiers to their respective maximum outputs. If there is any question, please consult your amp's manuals for something called "input sensitivity."

 

 





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