- Sidetone
=Telephony=
In
telephony , sidetone is the effect of sound that is picked up by the telephone's mouthpiece and introduced (at low level) into the earpiece of the same handset, acting asfeedback . Sidetone in 19th century telephones varied, often being so loud as to discourage speaking loudly enough, and occasionally so loud as to throw the instrument into uncontrolled oscillation or "howling". Antisidetone circuitry incorporating the principle of thehybrid coil brought sidetone under control in the early 20th century, leaving enough to assure the user that the phone is really working, and allowing the use of a unitizedtelephone handset .Without sidetone, users do not hear their own voice in the earpiece, and may think the phone is not working. Too much sidetone causes users to hear their own voice loudly. They may feel uncomfortable and lower the level of their voice.
Digital telephones lack the mechanical
acoustics and circuitry that created sidetone in older landline phones, so digital phones includeelectronic circuitry to reproduce the sidetone. Manycell phones do not provide adequate sidetone. Usability experts believe this causes some people to shout or speak too loudly when using a cell phone. [http://www.jnd.org/dn.mss/minimizing_the.html] [http://www.npr.org/templates/story/story.php?storyId=4229967] Similarly, in military field operations in enemy territory, operatives can be encouraged to speak quietly by increasing the volume of the sidetone.Sidetone is useful for people using handsets but can cause
audio feedback inteleconferencing systems if not treated properly.Radiotelegraphy
In
wireless telegraphy (WT) andamateur radio , sidetone is the audible indication of a CW signal as the operator sendsMorse Code . Like thetelephony definition of sidetone, it acts as feedback to the operator that what they are sending is what is intended.It is designed to mimic the tone generated by a typical radio receiver when a CW signal is converted to the
intermediate frequency (IF), then mixed with the BFO frequency to generate a "difference frequency", which is audible over the radio receiver loudspeaker or headphones.ee also
*
Telephone
* Beat Frequency Oscillator
*Continuous wave
*Echo cancellation
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