4305-DEMO THAT Corporation, 4305-DEMO Datasheet - Page 18

• 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

Page 18 of 20
companding system (neglecting the effects of R6 and
R12). As before, the columns labeled Encoder VCA
Gain, Encoder Out, Decoder VCA Gain, and Decoder
Out use the equations derived previously in the
section titled "The Mathematics of Log Based
Companding Systems".
labeled RMS In are derived using the equation:
encoder and decoder of Figures 20 and 21.
compression and expansion ratios here are the same
as those of the previous circuits, but the frequency
shaping afforded by signal pre- and de-emphasis and
detector pre-emphasis make this a superior sound-
ing system.
about ±30 dB, which is well within specification, as
is the RMS detector input current.
Other Dynamics Processor Configurations
contained within the 4305 are applicable to a very
Encoder
(dBV)
-100
-10
-20
-30
-40
-50
-60
-70
-80
-90
20
10
In
0
Table 4 shows the transfer characteristics of this
I
Figure 22 tracks signal levels through the
In this application, the VCA gain ranges over
We have said before that the building blocks
Table 4. Hi-fi compander transfer characteristics
RMS In
Encode
(In dB)
Gain
VCA
=
-28
-23
-18
-13
12
17
22
27
32
-8
-3
(applies to low frequencies only)
2
7
10
( Encoder Out
R
RMS In
Encoder
Decoder
20
(dBV)
Out/
-11
-16
-21
-26
-31
-36
-41
-46
-51
-56
In
-4
-1
-6
)
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com
THAT Corporation; 45 Sumner Street; Milford, MA 01757-1656; USA
The values in the column
0.1841
0.1035
0.0582
0.0327
0.0184
0.0104
0.0058
0.0033
0.0018
0.0010
0.0006
0.0003
0.0002
I
(mA)
RMS In
Decoder
(In dB)
VCA
Gain
-12
-17
-22
-27
-32
28
23
18
13
-2
-7
8
3
Decoder
(dBV)
-100
Out
-10
-20
-30
-40
-50
-60
-70
-80
-90
20
10
0
The
wide range of dynamics processor configurations.
These include companding noise reduction systems
with ratios other (higher or lower) than 2:1:2, multi-
band companders, etc. The 4305 is versatile enough
to be used as the heart of a compressor, expander,
noise
compressor, and many other dynamics processors.
It is beyond the scope of this data sheet to provide
specific advice about any of these functional classes.
We refer the interested reader to THAT's applications
notebooks volumes 1 and 2, which contain many
circuits based on THAT's other VCAs and RMS level
detectors, but are largely applicable to the 4305 with
only minor variations.
applications information aimed specifically at the
4305 in the future.
Closing Thoughts
companding systems is a very intricate art: witness
the proliferation of dynamics processors available in
the market today.
THAT's VCAs and level detectors, yet they all have
individual sonic characteristics. In the applications
section of this data sheet, we have offered a few
examples only as starting points. THAT Corpora-
tion's applications engineering department is ready
to assist customers with suggestions for tailoring and
extending these basic circuits to meet specific needs.
-100
-20
-40
-60
-80
The
20
Figure 22. Hi-fi compander transfer characteristics
0
gate,
In(Cmp)
design
Compression
THAT4305 Pre-trimmed Analog Engine®
AGC,
Process
of
Out Cmp
Many of these are based on
In(Exp)
de-esser,
dynamics
Of course, look for more
Expansion
Process
frequency-sensitive
processors
Out Exp
20
-20
-40
-60
-80
-100
0
and