THAT4301A Datasheet, PDF (11/12 Pages) List of Unclassifed Manufacturers – THAT Analog Engine® IC Dynamics Processor

THAT 4301 Dynamics Processor IC
Page 11
The GAIN control (R₁₈) is used to provide static
gain or attenuation in the signal path. This control
adds up to ±130 mV offset to the output of OA₂ (from
-V₊ ^R16 _R17 to -V_- ^R16 _R17), which is approximately
±20 dB change in gain of the VCA. C₅ is used to atten-
uate the noise of OA₂, OA₁ and the resistors R₈
through R₁₆ used in the control path. All these active
and passive components produce noise which is
passed on to the control port of the VCA, causing
modulation of the signal. By itself, the 4301 VCA pro-
duces very little noise modulation, and its perfor-
mance can be significantly degraded by the use of
noisy components in the control voltage path.
Overall Result
The resulting compressor circuit provides
hard-knee compression above threshold with three
essential user-adjustable controls. The threshold of
compression may be varied over a ±30 dB range from
about –46 dBV to +14 dBV. The compression ratio
may be varied from 1:1 (no compression) to ¥:1.
And, static gain may be added up to ±20 dB. Audio
performance is excellent, with THD running below
0.05% at middle frequencies even with 10 dB of com-
pression, and an input dynamic range of over
115 dB.
Perhaps most important, this example design
only scratches the surface of the large body of appli-
cations circuits which may be constructed with THAT
4301. The combination of an accurate,
wide-dynamic-range, log-responding level detector
with a high-quality, exponentially-responding VCA
produces a versatile and powerful analog engine. The
opamps provided in the 4301 enable the designer to
configure these building blocks with few external
components to construct gates, expanders, de-essers,
noise reduction systems and the like.
For further information, samples and pricing,
please contact us at the address below.
THAT Corporation; 45 Sumner Street; Milford, Massachusetts 01757-1656; USA
Tel: [phone]; Fax: [phone]; Web: www.thatcorp.com