4305-DEMO THAT Corporation, 4305-DEMO Datasheet - Page 9

• Manufacturer Part Number: 4305-DEMO
• Description: Audio Modules & Development Tools Low-Cost Dynamics Processor Demo Board
• Manufacturer: THAT Corporation

Specifications of 4305-DEMO

• Description/function: Audio DSPs
• Operating Supply Voltage: 15 V
• Product: Audio Modules
• For Use With/related Products: THAT4305
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Document 600067 Rev 01
we can state that:
adjust the point at which input and output levels of
the compressor or expander become equal. These
are a) adjusting the 0 dB reference voltage level of the
RMS detector by setting its voltage-to current
converting resistor (R1 in Figure 2), and b) varying
the static signal-path gain offset (A
the best practice is to achieve level match via a
combination of setting the RMS detector's voltage-to-
current conversion, and offsetting the signal-path
gain. Signal-path gain can be offset by altering the
values of the VCA's voltage-to-current and current-to-
voltage resistors. Both of these approaches have the
advantage of being temperature-independent.
of Figure 6 with varying sidechain gain k for a
constant A
compression ratio increases, and the dynamic range
of output levels decreases. Low input signal levels
(including noise) are increased, and high input signal
levels are decreased. Figure 9 shows how the same
compressor behaves with varying LM
and k. Note that as LM
decrease, and vice-versa.
transfer characteristics of the expander of Figure 7
change while varying k (Fig 10) and LM (Fig 11). In
each case, all other parameters remain fixed.
In
Similarly, for the expander shown in Figure 7,
Out
G
Out
In both Figures 6 and 7, we show two ways to
Figure 8 shows the behavior of the compressor
Figures 10 and 11 show how the input-output
dB
dB
dB
dB
Figure 7. Feedforward expander with level match.
dB
In
L.M.
+
dB
dB
-
RMS
= k(In
dB
dB
Σ
= In
= (1 + k)In
and LM
dB
dB
dB
-A
− A
− L.M.
dB
dB
. Note that as k increases, the
dB
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
k
dB
dB
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
is reduced, all output levels
+ G
− k $ L.M.
dB
)
. Thus:
dB
G
dB
dB
). For the 4305,
dB
dB
, but fixed A
− A
Out
dB
dB
dB
-100
-140
-100
-120
140
100
-100
-120
-20
-60
-20
-40
-60
-80
-20
-40
-60
-80
-20
-40
-60
-80
60
20
40
20
20
0
0
0
-120
-120
Figure 8. Compressor input-output transfer
Figure 9. Compressor input-output transfer
Figure 11. Expander input-output transfer
Figure 10. Expander input-output transfer
k=1
-60
-60
LM= -40
characteristics with varying LM
-100
characteristics with varying LM
-100
characteristics with varying k.
characteristics with varying k.
-50
-80
-80
-40
-40
-60
-60
dB In
dB In
dB In
dB In
-30
-40
-40
-20
-20
L.M.= -10
L.M.= -20
L.M.= -30
L.M.= -40
-20
-20
k=0
k=1
k=2
k=3
L.M.= -10
L.M.= -20
L.M.= -30
L.M.= -40
dB
dB
-10
k=0
k=1
k=2
k=3
Page 9 of 20
0
0
0
0
20
20