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Posted by Smarty on 04/28/07 13:27
Glad to help Rick, On point number 2, just to clarify.....it is very common
to apply "pre-emphasis" to boost high frequency (treble) content of audio to
reduce the apparent noise, and thus most TV and FM transmitters have a
built-in pre-emphasis circuit / boost. (AM broadcast transmitters generally
do not.) The same method is used in vinyl LP recordings as well as many
recent modulation techniques including Dolby and DTS.
If an outboard modulator like your Cadco also has a switchable built in
pre-emphasis, and by mistake it is kept turned "ON", while using the
transmitter's pre-emphasis as well, then you will have far too much treble
boost. The solution is to disable the switchable one in either place.
Good luck and happy hunting!
Smarty
"Rick Merrill" <rick0.merrill@NOSPAM.gmail.com> wrote in message
news:ZaKdneJjG84Goa7bnZ2dnUVZ_hKdnZ2d@comcast.com...
> Smarty wrote:
>> Four more thoughts:
>>
>> 1, The MTS-4 has both an audio output jack on the rear which will allow
>> you to hear / scope the audio before it hits the modulator. Connect up at
>> this point to determine if the compander is at fault.
>>
>> 2. The Cadco modulators have an internally defeatable pre-emphasis curve
>> which may be set for compensating highs. Be sure this is set correctly.
>>
>> 3. The MTS has a lot of output voltage and could be adding 10 DB or more
>> gain after beyond the companding. Make sure that your compander output is
>> not way beyond your modulator's input range (this is nappy's point, but
>> is more specifically relevant since the MTS puts out a big signal....)
>>
>> 4. Lastly, the compander has a remarkably narrow 5Khz bandwidth, quite
>> adequate for a call in talk-show telephone line or AM radio microphone,
>> but not much else. Take the compander out of the circuit altogether and
>> see how the wider bandwidth audio sounds with respect to sibilance and
>> let us know. We should then be able to help you further.
>>
>> Smarty
>>
>
> Thanks very much for that analysis! It should give me a fighting chance!
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