The Electromyograph or EMG signal is associated with the activation of thousands of tiny muscle strands making up a muscle or muscle group. This signal generally takes the form of many high frequency sinusoids summed together. The EMG is usually measured using a skin surface electrode placed at either end of the axis of motion of the muscle. The size of the EMG response depends on a number of factors, including the distance between the electrodes as well as the size of the muscle under examination. Certain facial muscle groups have been found to have considerable psycho-physiological signifiance.

It is desirable at times to record the "raw" EMG signal for later analysis. However, this method requires an extremely high sample rate, with a corresponding increase in the amount of memory required in order record the EMG signal for a reasonable time. If the magnitude of the EMG response for a particular muscle is all that is required, "Precision Rectification" can be applied to the amplified EMG signal. The precision rectification process supplies just the positive "envelope" of the EMG signal. This approach is called a "contour follower" in the literature. This approach benefits by requiring a much slower sample rate, and so enjoys extended recording time, when compared to recording the "raw" EMG signal.

We recommend the use of our Fetrodes for all EMG signal conditioning and recording systems.

The Biolog can record a number of EMG channels both with and without the Precision Rectification included.

The 2124 Fetrode amplifier can supply EMG signal conditioning, with or without the Precision Rectification, for your existing data acquisition system. The 2283FTi Fetrode amplifier can supply Raw EMG only.

Our SC2000 Simple Scope PC based data collection system can also be configured for Fetrode EMG -- but only with Precision Rectification.

Precision Rectified EMG can be supplied as a channel on our Multi-Subject Data Collection System.

If you are still not sure, drop us a line, and let us help!