Stereo Tool

The Trace Alpha sound card has 2 different outputs. It would be handy in some cases to be able to send composite FM from 1 output and asymmetrical AM modulation with 10khz band limiting to the other output. This would allow an AM/FM simulcast to be fed from 1 ST system.

Very interesting idea... Unfortunately the processing for AM and FM is different so this is not as easy as it seems. Running 2 copies on 1 system could be the solution, but you cannot use ASIO from multiple programs simultaneously, so to make this work it HAS to be done in one ST instance.

Giving up the Asymmetrical output would solve part of it (there are AM purists who believe that asymmetrical modulation is harmful to audio quality anyway) and moving the frequency response filter to the output side of the equation would solve the AM bandwidth issue. Whether it could be used to feed the same processing with separate frequency response limits is the question. If the filter killed everything above 10khz, the stereo pilot, 38K subchannel and RDS could in theory remain operational without ever reaching the transmitter. I'm not sure how many would ever use this but I could see those with AM/FM Part 15 systems in the US taking advantage of it. And there are some AM/FM simulcasts here as well.

As an offshoot of this topic, having separate Output Level adjustments on each of the two Trace Alpha outputs would prove quite useful. It's very common for 1 processor to drive 2 STL's or 2 transmitters and the level required is often different. Most of the newer processors (from the Orban 8200 forward) have 2 Composite Outputs with separate gain controls for each. Whether the AM idea ever sees the light of day or not, using that second output to drive the backup transmitter would definitely prove useful it it's a simple thing to implement.

It is similar thing where you have "normal" and "FM" output, where you cannot avoid FM pre-emphasis to not-be at "normal" output.
Ofcourse, it's possible, but you will need double processing. Look at Omnia.9.
Then AM/FM outputs are also possible.

For once the FCC saved the day on this one...in the US, the pre-emphasis for AM and FM is the same except that there's a 10khz filter on the output of the processor. So the second output of the sound card could already be used for AM as long as an outboard NRSC (10khz) filter were in place after ST. If the 10khz filter could be applied to the output of one side of the ST sound card, it could do AM and FM simultaneously. It would be convenient to have a separate output level adjust for the second channel but there are ways around that if that's the only thing that isn't practical.

Ok, i dont know much about AM, but is it normal to have FM pre-emphasis for AM output?

There are some disadvantages to doing this:
- Clipping needs to be different if you lowpass filter at 10 kHz, you cannot just do that afterwards.
- Compressor (MB and SB) behavior will be slightly different if you don't LPF the audio
- For mono AM broadcasts, using Stereo Image to convert from stereo to mono gives a much better result than just using a normal mono signal. This happens very close to the start of the processing, so if you turn it on then everything from that point on needs to be processed 'double' (once for FM, once for AM).

If quality an loudness (constant peak level) isn't very important this could be an option...

This isn't anything I actually need...just something that I had thought about from time to time. That said, if it were to magically appear, I probably would find an AM transmitter to play with

This is also useful idea for two separate FM instances sharing one sound card. (ST1 composite > Card L output, ST2 composite > Card R output). BBP does this, but I recall had some issues on my system.