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TOPIC: Buffer / Clocking problems?

Buffer / Clocking problems? 8 months 1 week ago #34052

  • geoffmartin
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Hi,

I'm using an HA-DSP with a MacBook Pro (13", early 2015) and OS 10.12.6. The HA-DSP is connected via USB audio, and I'm currently using it with all EQ's set to 0 dB gain...

I'm testing the headphone output of the device using a TPDF dithered, -1 dB FS sine sweep that runs from 20 Hz to 20 kHz over 60 seconds. The file is a 44.1 kHz / 16-bit wav format (although I've tried other sampling rates and bit depths). I'm playing using both the Apple Finder "preview" as well as Audirvana. The Audio MIDI setup is set to send 44.1 kHz, 2-ch, 24 bit (although I've tried other settings here and I'm seeing the same problem. )The problem does not exist on the same computer using the built-in headphone output. (Note that the same artefacts are present when I play from the Mac's Tidal application directly to the HA-DSP - but they're potentially difficult to hear, depending on the music's content...)

I've ensured that this is not caused by the volume setting on the HA-DSP or the Mac's internal volume setting.

When playing the file, there are easily-audible click's in the signal. These are at random intervals and appear to be either
- buffering problems
- some kind of clocking problem
- artefacts similar to, but worse than a typical skip/insert strategy.

These are happening simultaneously on both channels of the output.



Above is a screenshot of a recording of the problem, showing two instances. This was recorded using a semi-pro sound card connected to a second Mac (to avoid any blame of conflicting clocks causing the problem) using Audacity.

Any thoughts on (1) the cause of this and (2) the possible solution?

Thanks
-geoff

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Buffer / Clocking problems? 8 months 1 week ago #34112

  • devteam
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@ Geoff

Sorry for the late reply.
This is very odd and unfortunately not something we;re able to see here with the AudioPrecision..
I think that it would be very valuable for our engineers to get the same setup here (though we don't have an Imac from 2015, only macbook Pros and mac minis). Would you mind to please start a tech support ticket with our team? (support.minidsp.com)

We can take it from there to figure out what is this issue.

devteam
MiniDSP, building a DIY DSP community one board at a time.
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Buffer / Clocking problems? 8 months 1 week ago #34126

  • geoffmartin
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Hi,
Thanks for the response. I'll make an official ticket.
Just a small comment that this is not something that would normally show up with an Audio Precision, since it's not periodic.
The fastest way to detect this is to listen to a swept sine tone.

Also note that I'm also running on a MBP - not an iMac. I can try it with a 2011-mode 15" as well, just to verify that it's happening on both machines.

cheers
-geoff
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Buffer / Clocking problems? 8 months 4 days ago #34185

  • devteam
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@ Geoff

Thanks for the info. Our team received your tech support ticket and will forward the info to the engineers. We have few headphone amps here streaming music on our stations for our staff(not using Macbook pro but Win to stream though) and don't have the issue. Engineers will look into if they can reproduce it on Macbooks.

DevTeam
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Buffer / Clocking problems? 4 months 1 week ago #35917

  • FabianB
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Hello!

This is my first post on this forum.
Unfortunately it's because I experience the same problem. It is always present when I listened through the USB connection and using any DSP.
With the latest "crossfeed" beta software I experienced this clocking/buffer/jitter problem much more when the first stage of the cross-feed-processing were activated, the lowpass filter.
Also low frequency FIR/phase linear-filter exaggerate this problem. Maybe it's inherent to some kind of resampling to the DSP's (I guess it is) internal 96kHz sampling frequency?
I don't experience the same distorsion when using an analogue input to the HA-DSP.

/ Fabian,
enthusiast headphone listener and broadcast engineer from Sweden
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Buffer / Clocking problems? 4 months 1 week ago #35945

  • devteam
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@ Fabian

Very odd.. The issue of that pop was indeed solved in the latest firmware. Did you confirm that it's exactly the same?
Maybe best that you contact our team directly. We'd need:
a) Your DSP configuration file
b) Confirmation that you're running latest firmware + software (i.e. CF) with a restore to default all..

Thanks!

DevTeam
MiniDSP, building a DIY DSP community one board at a time.
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Buffer / Clocking problems? 4 months 1 week ago #35949

  • geoffmartin
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Hi,
I've changed my opinion since the latest update. As I emailed to the DEV team, I believe that this issue is not caused by clocking problems, but by noise on the volume controller.

My guess is that the volume knob is a simple voltage divider whose output is connected to an ADC. It appears that the "click" sound is just a gain switch caused by noise at the input of that ADC to bang back and forth between two values on the ADC - or at least the gain value.

One way to see if this is the same with you is to do the following:
1. play a mid-frequency sine tone (say, 997 Hz)
2. play with the volume knob. (Notice if the clicking sound that you hear caused by the gain changes is the same as the one that you hear as the artefact in question)
3. after increasing and decreasing the volume a couple of times, let go of the volume knob. Check to see if the clicking continues.
4. Repeat steps 2. and 3. to try again.

I can invoke the problem by repeating steps 2 and 3 fewer than 10 times.

Assuming that my guess regarding the source of the problem is correct, then the solution is to put a hysteresis function on the gain change to prevent it from trying to change back and forth between two gain values. Smoothing the gain change will cover up the problem, but not solve it.

Cheers
-geoff
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