USB noise or ground loop?

[Bassman59]

I'm noticing some confusion here between asynchronous USB transfers, that don't exist, and isochronous transfers. As far USB is concerned, there are two types of transfers for massive data: bulk and isochonous. Both have CRC verification, but only bulk guarantees correction (i.e.: data is delivered, if not, rinse and repeat until it is). Other types of transfer exist for control and signaling: control and interrupt transfers. Hope this little bit of information is useful.

I apologize — when I wrote above that USB audio uses asynchronous transfers, I should have been clearer and said that it uses isochronous transfers that in turn use one of three synchronization modes, which are asynchronous, synchronous and adaptive.

[bloguetronica]

I'm noticing some confusion here between asynchronous USB transfers, that don't exist, and isochronous transfers. As far USB is concerned, there are two types of transfers for massive data: bulk and isochonous. Both have CRC verification, but only bulk guarantees correction (i.e.: data is delivered, if not, rinse and repeat until it is). Other types of transfer exist for control and signaling: control and interrupt transfers. Hope this little bit of information is useful.

I apologize — when I wrote above that USB audio uses asynchronous transfers, I should have been clearer and said that it uses isochronous transfers that in turn use one of three synchronization modes, which are asynchronous, synchronous and adaptive.

Thanks for clearing that up. The asynchronous/synchronous/adaptive business seem to be a specificity of the audio class devices. Yes, the transfers would still be isochronous.

Anyway, I still bet that this has not to do with jitter. What the OP is experiencing is a ground loop.

Kind regards, Samuel Lourenço

[NiHaoMike]

VLC (the video player) has a feature that allows one to resample audio to the achieved display frame rate.  It is surprising how small changes in the actual pitch are perceptible -- in that case, because the video frame rate was not stable, so the resampling ended up changing the audio pitch by accident.  It is a surprisingly easy to notice very small changes, if the display frame rate is not rock solid stable.

You can use HDMI audio so that both the audio and video are sourced from the same master clock. The disadvantage is that HDMI is really hard to isolate.

[drummerdimitri]

I've switched to toslink connection but I still get crappy noise from the amp using my sensitive IEM's while my studio monitor's balanced XLR cables are connected to the preamp section.

This issue is becoming a nuissance as I've not yet found a solution. Would an isolation transformer do the trick? Will I need three? One for the preamp an one for each speaker? 

[magic]

Any balanced HP output there?

Does it make a difference if the monitors are connected to mains or not?