Stereo Tool

I have the latest Stereo Tool version operating in a Windows 7 Professional 32-bit computer with a 3.4 gig processor and a Corsair SSD. I am using an M-Audio Audiophile 192 sound card set for 192 in and out. Stereo Tool works well except for my stereo pilot injection. Although it is set at 8.5%, it varies from 0 to over 12% in a half-second cycle. As a result, I barely have any separation on the air. (My output is a 1/4" to BNC adapter plugged into the left main output of the sound card.) Also, the audio is certainly loud but I haven't found a preset yet that has enough treble (pre-emphasis is set to 75 us). What am I doing wrong? The end goal here is to use ST with its neat declipper to process current overclipped rock music.

Can anyone offer any suggestions? I have high hopes for this and will register it as soon as I can get it to behave!

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Just to eliminate the obvious, are you sure you have turned off any internal pilot on your exciter? I have seen that exact issue where the exciter's stereo on-off control did not actually turn off the pilot; the engineer had to go in and move jumpers. The two pilots mixing did make for a nice 1970's pseudo-quad 'Santana' effect, hah.

I think Doctor_Technical is right, it makes sense: If the 2 pilots are 'slightly' off in frequency you'll get some weird effect where they increase each other at some moments and cancel each other out in others. So there's probably a 2 Hz difference in frequency between the two.

For lack of highs, you could check these two things:
1. Did you enable 'Pre-emphasize output' in the FM settings panel? If not, the output sent to the transmitter is de-emphasized (!) and you'll have very little highs.
2. If your input level is really low, make sure to correct the Input gain (input sound card settings). If you don't the AGC won't work properly and the noise gate will be far too aggressive.

If it's not this, let's first wait what happens if the pilot is fixed - if stereo coding is enabled that must also mean that the transmitter itself is doing stereo encoding, and then it also needs to filter out certain high frequencies etc.

Sure enough, a dip switch was incorrectly set. That cured the pilot issue.

Next question... In the Input and Output boxes on the bottom of the screen, is it normal for the output to look extremely dense? I am wondering if I am overdriving something and thus would have difficulty getting the clippers to perform properly.
I am now getting a better tonal balance, probably as a result of not having dueling pilots!! TX pre-emphasis is on, BTW.

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That depends on the preset - but you can go extremely loud with Stereo Tool before things start to sound bad. So dense doesn't have to be an issue - if it sounds good it's ok.

O and it's normal that the clipping looks extremely tight, much tighter than with almost any other processor (especially if you enable the composite clipper) - that's actually a good thing because it means no volume is lost for no good reason.

OK, I've been playing with my ST installation for a couple of days and am really liking what I hear... except for a lot of hiss! One thing that I find strange is on the FM Transmitter page, Pre-Emphasis is on two separate buttons. Do I need to select both? My signal source is the same one that is feeding my regular transmitter and I don't hear any hiss there. My sound card is set for 192k in and out.

Also, to get 105% modulation out and show 8.5-9% pilot injection, I had to raise the total output enough that I ended up with almost 10% pilot. I had to turn the pilot down to 8% to get a reading of 9% on my modulation monitor.

In case I didn't state this before, this installation will be on a commercial high powered FM playing "Active Rock" as it is referred to.

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Hi Phil...what I gather is that if the bottom premphasis button is not clicked, the input is pre-emphasized and the output is de-emphasized. Both of mine are clicked and that sounds great. With Pre-emphasize Output un-checked, it sounds very dull.

If you have the Marian Trace Alpha soundcard, this will work great on a full power station. Only thing is, if there are live jocks and they monitor the air signal in their phones, the delay will immediately generate complaints from them. It's pretty much impossible to speak through ST and monitor it coming back over the air. Small price to pay for $10,000 worth of sound for a few percent of that

I'm aware of the inability to monitor OTA. I can work around that. The hiss is a deal breaker, though. The card I have is an M-Audio Audiophile 192 that, in spite of what I've read around here, has great bass response. My modulation control is very good, better than the Optimod currently in use.

The MTA card is not easy to find, while the M-Audio was.

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That hiss obviously shouldn't be there. So, we need to check where it comes from.

If you use Normal Output (you can send it to the built-in sound card of the pc for example), do you hear the hiss there as well? This is the de-emphasized and demodulated output signal, so it should be identical to what you hear on FM.

On the transmitter, does the hiss disappear if you disable the stereo coder? It could be that there's some high frequency hiss in the sound card that's normally not audible; when you enable the stereo pilot the signal around 38 kHz is mapped to the audible range in the tuner.

Are you using sound card input to sound card output or some other path with virtual cables or pipelines?


If this doesn't help, how much is a lot? I do get some mild hiss when I use the built-in sound card of my laptop to generate an MPX signal - as soon as there's any real audio present and I'm not broadcasting silence or only bass it's no longer noticeable.

I'll try listening to the Normal output tomorrow. The transmitter is a Elettronica TEX-1000 that we have as the ultimate backup to our five FM's. It is set to "mono" to keep the pilot turned off. See the discussion above.

I am using sound card input to sound card output. And, the hiss is plainly audible... and there is no hiss through the Optimod on the main station.

I'll also listen to the signal with the pilot turned off.

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