More Quirks of the PreSonus Studio 26c

A little over a year ago, I posted about some unexpected behaviour with the different output channels of the PreSonus Studio 26c. During my work of testing different audio DACs and receivers for audio latency, I noticed that the internal clock on this USB audio interface to be notably off compared to other audio devices I had. To verify this, I generated a simple test signal that had tick sounds at the 1 and 11 second mark with a constant tone played throughout. I played this test signal in WASAPI exclusive mode when on a Windows computer or using the default/built-in audio player on other devices and recorded the results using my onboard audio and the PreSonus Studio 26c. I then subtracted the number of recorded samples from 480,000 which was the expected number of samples for these recordings.

Output DeviceRecording Length: ASRock Z170 Extreme7+ Onboard (Samples)Error (Samples)Recording Length: Presonus Studio 26c (Samples)Error (Samples)
ASRock Z170 Extreme7+ Onboard480,0000479,91981
Presonus Studio 26c480,081-81480,0000
2013 Macbook Pro479,98614479,90694
Samsung Galaxy S8479,9946479,91387
iPhone SE Gen 1479,98812479,90892
Marantz NR1711 USB Playback479,9991479,91882
MSI GF75 THIN Laptop479,98020479,899101
Sony STR-DH540 USB Playback479,9982479,91783
Number of samples recorded for a 10 second 48 kHz signal.
Expected samples: 480,000

It seems quite clear that the Studio 26c internal clock is quite an outlier compared to any device I could find to test with. Thankfully this did not affect my results at all during my audio latency testing because the difference in clock was too small to affect a <100ms recording. But this type of offset could become substantial after only a few minutes of recording or playback!

These results seem to show that my ASRock onboard audio clock and the clock used in my Marantz and Sony receivers are effectively the same. If these three were assumed to be a “source of truth”, this would mean that the PreSonus Studio 26c clock is actually running at 47.92 kHz when it says it is running at 48.00 kHz. As expected, this inconsistency appeared in other sample rates as well. Simply stretching the audio by 1.00016875x will correct the recording to be closer to the intended sample rate.

In the control panel for the PreSonus, there is an option to choose which clock source the device uses, but unfortunately the only option that was available to me was to use the Studio 26c internal clock. I presume that higher-end PreSonus devices allow use of a different clock through this setting to make recordings and playback consistent between devices.