IMPORTANT: The 4301 is not recommended for new designs


• High Performance Blackmer®
Voltage Controlled Amplifier (VCA)
• High Performance RMS-Level Detector
• Three General-Purpose Opamps
• Wide Dynamic Range: >115 dB
• Low THD: < 0.03 %
• DIP and Surface-Mount Packages

Datasheet Download

Datasheet Download
4301 Datasheet (765 kB)
Analog Engine Dynamics Processors


• Compressors
• Limiters
• Gates
• Expanders
• De-Essers
• Duckers
• Noise Reduction Systems
• Wide-Range Level Meters


THAT 4301 Dynamics Processor, dubbed “THAT Analog Engine®”, combines in a single IC all the active circuitry needed to construct a wide range of dynamics processors. The 4301 includes a high-performance, exponentially-controlled Blackmer® VCA, a log-responding RMS-level sensor and three general-purpose opamps.

Key Specifications(see4301 datasheetfor complete specifications)




Power supply voltage


± 15


Supply current




Dynamic Range




Gain Range


< -100 to > +30


Total Harmonic Distortion

+10dBV, 1 kHz, 0 dB gain



Control Constant (both positive & negative- sense control available)


± 6.5


Output Noise

0 dB gain



RMS Detector
Averaging Method


Root Mean Squared (RMS)


Output Scaling




Dynamic Range


> 80




> 20


Crest Factor

1 dB reading error



Input Offset Voltage


± 0.5


Input Bias Current




Gain-Bandwidth Product




Slew Rate




Input Voltage Noise

OA1 OA2, OA3

6.5 7.5


Packaging / Pricing / Samples
Model Package Order Number Pricing (1000) Min Order Quantity Samples
4301 20 Pin DIP 4301P20-U $5.35 20 Request Samples
20 Pin SO Wide 4301W20-U $4.94 37
4301 Demo Board 4301DEMO $100 1  
All 4301 parts are RoHS compliant. Minimum Order Quantity (MOQ) is one tube or one reel. Parts must be ordered in multiples of the MOQ. Samples are available for qualified applicants. Pricing is subject to change.

Design Notes (as PDF files)

Design Note 00A   Basic Compressor/Limiter Design (113k) (formerly Application Note 100A)

Design Note 01A   The Mathematics of Log-Based Dynamic Processors (64k) (formerly Application Note 101A)

Design Note 02  Digital Gain Control with Analog VCAs (106k) (formerly Application Note 102)

Design Note 03  Signal Limiter for Power Amplifiers (95k) (formerly Application Note 103)

Design Note 04   Improving Loudspeaker Signal Handling Capability (217k) (formerly Application Note 104)

Design Note 05   A Low Parts Count, Two-Slope Compressor (78k) (Application Note 105)

Design Note 100   A Fully Adjustable Noise Gate (69k)

Design Note 101   Peak Detection with the THAT4301 (37k)

Design Note 102   Adjustable Ducker using the THAT 4301 (76k)

Design Note 107/111   A Simple Effective Soft-Knee Compressor / Limiter (81k)

Design Note 108   Single Chip Automatic Gain Control  (73k)

Design Note 112   LED Bar-Graph Compression Indictor (83k)

Design Note 113   THAT4301 Gain Reduction Indicator (33k)

Design Note 114   Adaptive Attack and Release Rates using THAT RMS Detectors (48k)

Design Note 115   Fully Adjustable Compressor/Limiter (46k)

Design Note 116   Techniques for Stereo Volume Control (126k)

Design Note 117   Input Limited for ADCs (120k)

Design Note 118   High Performance Stereo AGC (90k)

Design Note 119   Wide Ranging dB Meter (177k)

Design Note 125   The “One Knob Squeezer”  (90k)

Design Note 128   What’s a PTAT Temp. Coefficient, & Where Does It Come From?  (64k)

Design Note 131   Dealing with the PTAT Coefficient (75k)

Design Note 132   Alternate Method of Indicating Compression (52k)

Other Analog Engines  
THAT 4305 Low-cost basic Analog Engine for dual supply voltages. 4305 Datasheet
THAT 4320 Low-voltage, low-power versatile Analog Engine for single supply voltages. 4320 Datasheet
THAT 4315 Low-voltage, low-power basic Analog Engine for single supply voltages. 4315 Datasheet
THAT 4316 Very low-voltage, low-power basic Analog Engine for single supply voltages. 4316 Datasheet
Voltage Controlled Amplifiers (VCAs)  
THAT 2180 Series Pre-trimmed Blackmer VCAs 2180 Series Datasheet
THAT 2181 Series Trimmable Blackmer VCAs 2181 Series Datasheet
THAT 2162 Dual Blackmer VCAs 2162 Datasheet

Additional Resources

Analog Engine Selector
A side by side comparison of the features and specifications of our Analog Engine dynamic processor ICs.

4301 Device Model
Our SPICE macro models allow modeling of the important parameters of our ICs.

4301 Demo Board– The THAT 4301 Demonstration System (US$100) allows the engineer to test the performance of a THAT4301 quickly and easily. The 4301 Demo Board is self-contained circuit board with XLR connectors for signal input and output and a 3-pin header for connection to an external regulated DC power supply (not included). See the4301 Demo Board Datasheetfor more information.

Harsh Environment Packaging– TT Semiconductor repackages THAT Corporation’s IC products in ruggidized plastic for the medical, aerospace, defense, and heavy industrial marketplaces.

The History of VCAs– THAT Blackmer® VCAs are the successors to the original dbx® line of VCAs. Their development for professional audio use has a long history, and can provide some insight into the care and feeding of these essential devices.

4301 Material Data Declaration Sheet
Material Data Declaration Sheets (MDDS) disclose the hazardous materials in our integrated circuits as required by the European RoHS directive.