Stereo Tool

Thanks. 48kHz is no problem as the station clock rate is 48kHz.

My On Air test with ST using MPX out of ST to the STL was not nice.

The problem was the FM buffer kept running out no matter how high I set it, even up to 5 seconds. I didn't have the Normal Output configured as I wasn't using it so had it turned off. I just setup and configured the FM Output. The MPX out of the receiver into MPXTool showed a Max Hold on the modulation of about 60 per cent. That was something we could have adjusted but the buffer running out caused us to terminate the testing.

The CPU only ever reached a maximum of 30% utilisation with FM, Encode Stereo, Encode RDS, 50us Pre-Emphasis, and Composite Clipper checked ON.

I am sure the issues are related to my lack of knowledge of the settings.

A bit of testing while writing this shows the buffer issues starts when I activate Composite Clipper.

Back to the drawing board.

Clipper

This happens when your CPU is not fast enough to handle the processing. You can try to deactivate the Declipper and/or Composite Clipper, or lower the clipper-strictness (advanced clipper-tab - CPU, not recommended when using Composite Clipper), or lower the latency (config-tab, but you will loose quality). Or lower the display refresh percentage (config-tab). AFAIK Hans is about to implement multicore support for the new composite clipper, maybe this will fix it too in the future...
There is a tone generator in the FM-Output-tab (output correction must be enabled to activate it). Choose 400 Hz sine and turn the Volume-slider up until you get 100 % modulation. If you're using BS412, this is very important to actually transmit BS412-compliant.

I have been able to run composite clipping on an i3 by changing some of the settings as mentioned by radiofreak.

Are all the cores of your i7 running at a maximum of 30%?

BTW, I have previously found the tone generator in 'Configuration - Soundcards - FM Output' very useful for setting level but don't recall having to have enabled output correction.

@radiofreak, thanks for the suggestions I will give them a try.

@2Sense, the core usage is 0=5%, 1=8%, 2=11% and 3=5%. That is the total usage not just for Stereo Tool. I wouldn't have thought that was maxing it out to cause the buffer issues.

I am still a little lost with the correct use of the Sample Rate setting. I am inputting audio at 48kHz but have the soundcard and ST Sample Rate at 192kHz for the MPX. Is that the correct usage?

Thanks.

Yes, this CPU usage doesn't seem unreasonable does it?

Do you have any issues playing 192kHz audio through the Audiophile 192 using a different application?

I guess you have already checked the OS soundcard settings and this is all fine? How about your VAC settings?

Are you using an ASIO or WDM driver to output the audio from ST? Possibly try changing this and see if there is any difference?

Issues (mostly) solved.

Got one of our engineering guys to come in and look at the issue. It was the sample rate setting.

He asked me if the Sample Rate section was the front End Sample Rate or the Back End Sample Rate. Seems from what made it work it is the Back End Sample Rate; with no Front End Sample Rate? I had no idea.

I started this testing using the audio off the fibre here and that is at 48kHz so the 192kHz would have been appropriate but when I moved the setup I used a patch cable and took a 44.1 audio feed and still had sample rate in ST at 192kHz. He told me to change it to 176.4kHz and it worked without any buffer issues at all, even with much smaller buffer times.

When I selected Composite Clipper the buffer dropped all the way down and the sound started to slow down. I turned off Advanced Clipper and the buffer restored but the output level dropped. When I turned off the Advanced Clipper I did notice the Composite Clipper went off too.

So with no Composite Clipper it all worked perfectly. The CPU still only reached a maximum of 30% utilisation with everything on.

Thanks to those who offered suggestions. I tried everything suggested. Now to chase down the Composite Clipper buffer issue.

Clipper

Clipper was quicker

Composite clipper CPU load can be really high, I'm still working on that. SSB should be ready tonight.