The TREC AUDIO MONITOR is available in two different versions: with and without integrated bandpass main amplifier filter (see figures 1 and 2).

Figure 1: TREC audio monitor with integrated bandpass main amplifier filter with selectable gain (x50…x5000) and fixed bandpass filter (500Hz…10kHz). This audio monitor is connected to the analog headstage/preamplifier signal output.

Figure 2: TREC audio monitor without integrated bandpass main amplifier filter to be connected to an analog main amplifier signal output.

Both versions of the TREC audio monitors offer advanced audio features like a noise suppression circuit that allows background noise reduction (e.g. reducing neural background noise while improving the quality of single unit sound).

Figure 3: Working principle of the squelch. (A) original spike signal, (B) squelch level selected with squelch control at the audio monitor front panel, (C) resulting discriminated signal in the loudspeaker. Low amplitude background hiss is removed.

Please find an audio file below that demonstrates the signal from the audio monitor loudspeaker. The audio file starts with the multi unit signal, then the threshold for the squelch is increased slowly to isolate the single units and to reduce the neural background noise. At the end of the audio file the threshold is reduced again to get the multi unit activity.

This type of audio monitor is frequently used in central nervous system recording. Each spike is heard as an audible click, and the rate and volume of clicking is a good indicator of nerve cell activity.

One use for the TREC AUDIO MONITOR is to listen to the neural signals while stimulating the neurons you can easily determine whether some sounds are correlated to your stimulation. You can then look at the oscilloscope to see whether you can pinpoint the features in the signal that correspond to the sounds you heard thus identifying the relevant activity within the recording.

Use the volume, bass, and treble controls on the AUDIO MONITOR to adjust the signal level and sound quality; these controls only affect the speakers and will have no effect on the signal that is recorded by the computer. Both speakers of the headphones will deliver the same sound. The Instrument is not intended for clinical measurements using human subjects.

Audio monitors are standard features in TREC neuroscience recording systems. To minimize the potential for aggravation, we include a headphone jack so that users can listen to the audio output without testing the patience of their colleagues.

Once electrodes are in place and the amplifier is turned on and in REC mode, spontaneous action potentials should be evident as fast deflections on the oscilloscope. You should also be hearing ‘pops and crackles’ coming from the audio monitors.