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."
