Electronics > Projects, Designs, and Technical Stuff
USB noise or ground loop?
Bassman59:
--- Quote from: bloguetronica on March 30, 2019, 02:48:24 am ---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.
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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:
--- Quote from: Bassman59 on March 30, 2019, 04:39:12 am ---
--- Quote from: bloguetronica on March 30, 2019, 02:48:24 am ---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.
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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.
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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:
--- Quote from: Nominal Animal on March 29, 2019, 07:08:43 pm ---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.
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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? :palm:
magic:
Any balanced HP output there? ;)
Does it make a difference if the monitors are connected to mains or not?
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