Stereo Tool

Hi!
I love your software, it makes my music sound very well, and i don't even do broadcasting

But to my question, what can I do to reduce the delay without buffer underrunning? CPU upgrade? Does soundcard have something to do with buffers?

I'm asking these things because I'm handling the radio broadcasting in airshow in Finland at 2010 or so, just planning to make sound better and with stereo and RDS, they experimented FM broadcasting in previous airshow with no processing whatsoever.. If there is delay, it would be horrible because the same sound what is coming through PA without processing (and delay)

Completely eliminating the delay is not possible. I don't know how much delay would be acceptable?

A small delay is probably no problem, because the sound from the PA system will also take some time to arrive (sound travels at about 340 m/s, so every meter in distance causes a 3 ms delay. At a distance of 20 meter from the nearest PA speaker that's already 60 ms. And a small difference between different sources is usually not annoying).


There are several things that cause delay:

- The sound card (or more accurately: Windows)
Make sure that you are using ASIO to reduce the delay from about 300 ms to about 10-20 ms. (!). To get such low delays, set the FM output buffer size to about 10-20 ms in the "Configure Sound Cards" window. (I'm assuming here that you are using the stand alone version of Stereo Tool, and broadcasting input coming from for example a microphone).

- All the processing
Firstly, enable "Low latency" (Select "Advanced mode", then it's on the bottom right). This will greatly reduce the amount of latency (almost by a factor 4).
Then, only enable the things that you REALLY need. Everything that you turn on will cause (some) extra delay. Loudness causes the largest delay, followed by the Multiband filter (which at HQ mode causes twice as much delay as without HQ mode). Final Pre Limiter and Final Limiter can cause HUGE delays depending on the number of ms they are configured to look ahead. The noise gate also causes a significant delay - but I can imagine that you really need it when using and compressing microphone input.

So, assuming that you don't need the extra loudness, set Loudness to 1.00. And turn Multiband HQ off.

About the sound card: IF your sound card supports ASIO, changing to another sound card will have very little effect.

About the CPU: ONLY if very low output buffer size settings cause hiccups (so you HAVE to increase the buffer size to get rid of them), using a faster CPU will solve that and allow using lower output buffer size settings. The effect of this is probably very small.


If output volume is NOT an issue, and you just want to get a reasonable constant signal, this is how to do it:
- Enable Low Latency
- Set Loudness to 1.00
- Set Multiband HQ OFF
- Set Stereo effects OFF
- Turn Final Pre Limiter OFF
- Set Final Limiter timing to 2 ms. Tune the volume such that you don't get too many spikes where compression occurs. (Especially important if you play music, for voices spikes are less noticable.)

RDS and Stereo cause little extra delay, so you should be able to use those without any problems.

Note: In the FM settings window, at the bottom you'll find a setting that determines whether the MPX signal is strictly kept within range. If you enable that, it will cause a very small delay. If you don't the MPX signal will cause peaks that could disturb neighbouring radio stations, and to avoid that you'll have to turn the broadcast volume down by about 10%.
If possible, avoid using the "FM Transmitter Calibration" - that will also cause some delay.