Increasing distortion on long recordings

[Rocking]

I have a big issue with my reaper.

When recording a live concert (stereo out, 2 tracks) after ~8 minutes the recording starts to slightly distort. Later on the the distortion gets bigger and bigger. After ~40minutes you cant't understand the music's pitch. After ~1 hour the record becomes just silent.

I'm recording 2 tracks on 44.1 khz, 24 bit. No FX. Jusing latest drivers. HDD isn't full.

System:
Macbook pro 13"
i7, 6gb ram
HDD is 7200 rpm

Sound interface - Tascam US-366

any suggestions?

[cyrano]

That's usually a sign that something in your audio chain isn't running at exactly the same clock as the rest.

Have you checked Preferences->Device in Reaper?

There is a checkbox "Request sample rate" and "Request block size". For some interfaces these need to be checked. Try checking "Request sample rate", of course with the correct value for your project's sample rate.

Normally, Core Audio will resample "automagically" and sometimes that turns out less than ideal.

Also, check "Audio/midi setup" and confirm all settings. Sometimes it looks OK, but it isn't.

[EDIT]

And it's always a good idea to split long recordings...

[Rocking]

The "Request block size" was checked, although "Request sample rate" wasn't. Could this be the issue?

[cyrano]

With some interfaces it's needed. Depends on driver and interface.