How to fix audio glitches / stuttering

[Mike Daniell]

Audio glitches or stuttering are probably due to "buffer underrun", which means the program is not filling the playback buffer fast enough from disk. You should find this will be fixed if you choose not to use the SCS Internal Mixer. The default playback buffer size when using the internal mixer is 200ms (it has to be short), but when not using the internal mixer the default playback buffer size is 5000ms.

Set the required options by clicking on General Options / Permanent Options and selecting the Audio Driver tab. Now select Do NOT use SCS internal mixer and make sure the buffering and update options on this tab are all set to SCS default.... I also suggest you clear the three checkboxes, unless you need to set any of them for other reasons.

The Audio Driver options tab should now look like this:



Then click OK to save the changes, and close and restart SCS.

There are, however, some limitations imposed when you do not use the internal mixer. The following features are NOT available when you choose not to use the SCS internal mixer:

• Downmixing stereo files to mono outputs, unless the stereo files are MP3
• Panning when using speaker outputs other than 'Front (Stereo)' or equivalent
• ASIO support
• In the meter display at the top of the main window, only VU Levels will be displayed - Frequency Graph, Frequency Bars and Waveform are not available.

[dcScena]

Hi, I have been following this thread and here's my dilemma: we have fades using all (5) outputs, and I am using the ASIO drivers to run our (Presonus Firebox) interface, so I need to use the SCS internal mixer.

I can't get the system to misbehave here at my studio, but it doesn't like the theater booth for some reason: cues skipping all over the place. And not just at the top of cues, which I had halfway expected.

I raised the pre-buffer and playback buffers from 200 to 300ms, defragged the (mostly empty) drive, disabled extra stuff including internet and networks other than FireWire, and the problem improved but did not go away. I raised those buffer values to 500ms and the problem became slightly worse. My operator is plenty smart but not an SCS expert (she can get into the settings menus and out OK if I talk her through it), I can't get access to the machine till Monday (to, what? put in a faster hard drive?) and meanwhile there are two shows to be gotten through. Are there any other settings changes (floating point? update period?) that could help get us through the next two shows? And that I can communicate to my booth person over the phone? My last instruction to her was to raise the buffer values to 750 and see if it helped or not.

Hardware: Dell Inspiron 600 laptop, SIIG (TI chipset) FireWire card, Windows XP Pro with latest SP, 1 GB memory, PreSonus Firebox (using wall-wart power supply). Oh yes, cues are mixed AIFF and WAV, but the system has Quicktime 7 installed.

Thanks in advance!

BTW regarding the M-Audio interface question: using "another" cue system on a Mac, we discovered the "noise out of outputs 3 & 4" problem after it blew a speaker. It seems to be just a property of M-Audio hardware as far as I can tell - I've sworn off. I like the PreSonus pretty well.

[Mike Daniell]

Do you have to use ASIO? I'm sure your playback will be clean if you switch to WDM and use the Audio Driver settings recommended in this topic.

[dcScena]

the problem is that now that the show is up and running, I only have access to the computer when the show is NOT running, so I'm limited to what I can tell the operator over the phone. (I live in another city!)

So I could certainly use the WDM rather than ASIO, but does that solve the panning problem?

thanks,
dc

[Mike Daniell]

So I could certainly use the WDM rather than ASIO, but does that solve the panning problem?

How does the Presonus publish it's outputs if you use WDM? Are they stereo pairs or just a single multi-channel output? If they are stereo pairs (eg outputs 1/2, outputs 3/4, etc) then panning will not be an issue. Basically, if not using the SCS internal mixer then you can pan provided you use the default outputs (front stereo or equivalent). If stereo pairs are used then you only have two 'speakers' per stereo pair. Panning is only an issue if you have to use a multi (more than 2) channel output and you want to use output(s) 3 or higher.

[dcScena]

OK, so left-right panning across any stereo pair is cool, but panning among 4 outs as if I had a joystick to do it with is not? Not that I want to.

Thanks for your replies - meanwhile my trusty operator tells me that the last trick we tried before I contacted you (using the internal mixer, and lengthening the play buffers to 750 ms) resulted in a skip-free show; are there any problems I should watch for? (I note the fadeout issues and have her watching for them already.) If I have any further problem I'll shift over to WDM outputs - and I'll certainly do it that way from the start next time. Thanks!

[dcScena]

OK, now that the show is down and I have the computer in my shop and can test it, I can finally clarify (BTW the show operator told me the stuttering never did completely go away after all): Contrary to my faulty memory, there are no "WDM" outputs coming up. SCW lists "PreSonus" outputs 1-2, 3-4, "Line out" and S/PDIF out in the SCS outputs listing - but I could only get signal out of the PreSonus channels 1 and 2 - nothing would come out any other output channels unless I activated ASIO. And there is a pair of channel 5 & 6 outputs that don't come up in the listing at all. Right now I have the system set up to use "PreSonus" outputs 1 & 2, and ASIO outputs for channels 3-4 and 5-6. It seems to be stable for the moment; tomorrow I will shake it down and see if I can get it to skip.

thanks, dc

[preeves]

I think this has been posted before, but DPC Latency Checker may be worth a look trying to fix audio dropouts;
http://www.thesycon.de/deu/latency_check.shtml

Thought this was worth adding to the topic,
Regards,
Paul

[Mike Daniell]

For the record, dcScena's issue was fixed after some investigation, using the WDM outputs. There was a bit of confusion regarding the Speakers/Outputs settings, which is what gave rise to the concern about only outputs 1/2 working. The Presonus publishes its WDM outputs as stereo pairs, so for each stereo pair it is necessary to specify 'Left and Right (Stereo)' as the Speakers/Outputs assignment, not something like Outputs 3/4.