Blackmer RMS detector information

The Blackmer RMS detector is an electronic true RMS converter invented by David E. Blackmer in 1971. The Blackmer detector, coupled with the Blackmer gain cell, forms the core of the dbx noise reduction system and various professional audio signal processors developed by dbx, Inc.

Unlike earlier RMS detectors that time-averaged algebraic square of input signal, the Blackmer detector performs time-averaging on the logarithm of the input, being the first successful, commercialized instance of log-domain filter.^[1] The circuit, created by trial and error, computes root mean squared of various waveforms with high precision, although exact nature of its operation was not known to the inventor. First mathematical analysis of log-domain filtering and mathematical proof of Blackmer's invention were proposed by Robert Adams in 1979; general log-domain filter synthesis theory was developed by Douglas Frey in 1993.^[2]