 Wiring a Telephone Microphone |
Formula 
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| quote: |
Originally posted by Surya
A telephone does bandbass. At least, it used to, I don't know if recent models do the bandpassing still.
The frequency of analogue telephones was, if I remember correctly, between 500hz and 3000khz (or 3500khz) |
The mic itself doesn't have that bandwith, it's a bandpass filter after the mic that keeps the signal between certain limits, to modulate it easier.
So the mic itself won't give you the telephone sound... 
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27-08-2005 18:15 |
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djfreemc
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To be a little more exact: a telephone cuts of everything above 6KHz, that's why they sound so crappy. The reason is to limit bandwith and technical problems, but not the modulation. A classic telephone signal is actually a plain audio signal with no modulation whatsoever.
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27-08-2005 22:44 |
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djfreemc
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Well this discussion is getting quiet 
, but anyway... Do you have any more info on what kind of modulation is used in telephone systems then? Because I don't know any. I took telecommunications as an option, and my teacher for telecom and datacom was an ex-belgacom engineer. And as far as I know there is no HF whatsoever on a classic telephone line. Before there was ADSL everywhere there where even filter coils in the telephone network keeping out everything above 6 KHz (and thereby reducing transmission line problems), so how would you modulate on HF then? Anyway, if you have more info on this, i'd be most interested to read it.
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28-08-2005 11:01 |
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Formula
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| quote: |
Originally posted by djfreemc
Well this discussion is getting quiet
, but anyway... Do you have any more info on what kind of modulation is used in telephone systems then? Because I don't know any. I took telecommunications as an option, and my teacher for telecom and datacom was an ex-belgacom engineer. And as far as I know there is no HF whatsoever on a classic telephone line. Before there was ADSL everywhere there where even filter coils in the telephone network keeping out everything above 6 KHz (and thereby reducing transmission line problems), so how would you modulate on HF then? Anyway, if you have more info on this, i'd be most interested to read it. |
Goddamned, you're right 
I was mixing up cell phones and classical phones 
'classic' telephone signals don't need to be modulated on a HF carrier, they go through copper wires, so their is no need to.
The audiosignal isn't modulated, but converted to a digital signal, and vice versa (ADC/DAC) This gives also a specific characteristic to the signal. (because the original signal can't be 100% restored after converting)
But from the moment you use a wireless phone or cell phone, it will be (FM) modulated on a HF carrier wave
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28-08-2005 13:35 |
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djfreemc
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| quote: |
Originally posted by Formula
'classic' telephone signals don't need to be modulated on a HF carrier, they go through copper wires, so their is no need to.
The audiosignal isn't modulated, but converted to a digital signal, and vice versa (ADC/DAC) This gives also a specific characteristic to the signal. (because the original signal can't be 100% restored after converting)
But from the moment you use a wireless phone or cell phone, it will be (FM) modulated on a HF carrier wave
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Offcourse it has to be modulated for a wireless system, or we would get one big signal jam. But unfortunately you are again not completely correct. The classic telephone system was invented long before anyone had ever heard of digital signals, so it isn't digitized either. On an ISDN line and modern cellphones it is. Not in the good old telephone system, and not even on the first mobile systems that never really got popular. A DECT system is actually combining digital and analog in a "strange" way. You speak is first digitized in the handset, send to the base station digitally and then turned back to analog to send it over the good old analog telephone line.
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28-08-2005 19:38 |
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GreatFisherCat
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Due bandwith saving princibles, even original land-line telephone call is nowdays digitized, if it requires to be sent from one phone switch central to another. So if you call to your closest neighbour (or someone else living in close), signal route MAY be pure analog (stays inside the analog switch central). If you call to another city, you can bet your hat the call is digital somewere along the way.
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02-09-2005 21:25 |
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djfreemc
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You're right about that! The only thing that remains analog is the piece of wire from your home to the central you are connected to.
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The mysteries of the distorted snare...
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02-09-2005 22:31 |
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Halph-Price
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03-09-2005 20:08 |
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Formula
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But, now that I think of it...
it has to be modulated, because multiple signals are being transferred through the same medium. If you don't modulate than, how will you know what's what?
i dunno, a question 4 the doc
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03-09-2005 21:48 |
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thechronic
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They use a multiplexer for that in the analog domain, digitally it's ofcourse no problem to send multiple conversations through the same cable.
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05-09-2005 14:41 |
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Halph-Price
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28-09-2005 19:20 |
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Halph-Price
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| quote: |
Originally posted by Formula
| quote: |
Originally posted by Surya
A telephone does bandbass. At least, it used to, I don't know if recent models do the bandpassing still.
The frequency of analogue telephones was, if I remember correctly, between 500hz and 3000khz (or 3500khz) |
The mic itself doesn't have that bandwith, it's a bandpass filter after the mic that keeps the signal between certain limits, to modulate it easier.
So the mic itself won't give you the telephone sound...
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it's is the microphone because it does only limited freq. it doens't have any moving diaphrams like condenser or ribbon or dynamic, it uses a solid material, and thus gives it incrediable duriblity. when i am at home i'll give you the siteing from the live sound book i got and explain better. but the type of material gives different sound, and it is why it sound slike shit. but this is desired since you only hear voices in a limited freq, and it helps elminate background noize.
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27-10-2005 19:29 |
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Halph-Price
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Piezo-Electric microphones ( and contact pickups) *like guitar pickups* invole the sue of a substance which, when twisted or otherwise fegormed by a force -- such as the pressure provided by a passing sound wave, generates a vocaltage (called a piezoelectric voltage). Crystal and ceramic micophones both utilize this principle.
Traditionally they are strong utility mics of poor sound quality ( used in telephnoes, for example). ya da yada, there are high audio uqality ones around, fasten to wood, or other vibrating plates. common in acoustic guitars by manufacturers, good with most stringed instrumnets.
this is from LIVE SOUND REINFORCEMENT
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01-11-2005 07:44 |
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