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Posted by Smarty on 04/29/07 18:10
Good. That eliminates the possibility that you are applying pre-emphasis
twice.
Smarty
"Rick Merrill" <rick0.merrill@NOSPAM.gmail.com> wrote in message
news:XvCdnaDLg5PQBqnbnZ2dnUVZ_gGdnZ2d@comcast.com...
> 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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