Microsoft LPF-00004 Manual del operador descargar pdf (Pagina 51)

PRINCIPLES OF OPERATION Page 33

YBER

380, COPYRIGHT MARCH 2002, AXON INSTRUMENTS, INC.

THRESHOLD

SQUELCH

THRESHOLD

SQUELCH

Figure 13. The audio monitor is active during the time indicated by the thick horizontal bar because the absolute

value of the signal exceeds one of the squelch thresholds (dashed lines). At all other times the signal level is within

the squelch thresholds and the audio circuit is disabled.

In TONE mode, the OFFSET control (physically the same control as SQUELCH) alters the base

frequency of the tone. For example, some users might prefer a -2 V signal to correspond to 1 kHz,

while others might prefer it to correspond to 200 Hz.

External Input

The selector switch in the audio monitor section allows the selection of any one of the eight signal

conditioning channels or an external input. The external input could be used: (1) to listen to spoken

comments previously recorded using a microphone and played back through the D/A converter of the

data acquisition system, or (2) to listen to background music from a radio or other source. The

advantage of playing the background music through the audio monitor of the CyberAmp is that the

music is automatically switched off whenever it is necessary to listen to the signal on one of the signal

conditioning channels. The disadvantage of listening to background music through the CyberAmp

amplifier is that the small speaker used inside the CyberAmp is not a high-fidelity speaker.

External Speakers and Headphones

A researcher might choose to use headphones rather than the internal loudspeaker for at least two

reasons. First, the audio monitor may annoy co-workers in the same room. Second, headphones

generally have a far broader audio bandwidth than small speakers. With good headphones, sinusoidal

frequencies as low as 20 Hz can be heard.

Headphones plug into the jack on the front panel. If stereo headphones are used, the same sound will

be generated in each ear-piece.

When listening to background music, or when more volume is required for listening to small

extracellular spikes, it may be desirable to use a better speaker than the internal one. A small high

fidelity speaker with an impedance of at least 4 Ω can be plugged into the headphone jack. If more

power is required, users should consider purchasing from an audio store a speaker with a built-in

power amplifier.

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Microsoft LPF-00004 Manual del operador Pagina 51