Posted by Rick Merrill on 04/29/07 13:19

Smarty wrote:
> 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


We have already removed the internal jumper in the Cadco in order to
work with the BTSC encoder (that jumper is for the purpose of removing
preemphasis).

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