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An "objective" test of the ifi iPurifier3 (I tried)

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Nov 27, 2021
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I tried to do an objective test of the ifi iPurifier3 as doing a proper blind ABX listening test would require two of the same DAC.
Thought process was sort of stolen from a video made by Passion for Sound where he compared usb cables to each other by recording the DAC output with a USB audio interface.
20211127_122506.jpg

My goals with this experiment were:
1. To improve upon the testing method that Passion for Sound developed
2. Determine if there is an objective difference between using the iP3 and not
Equipment used:
-Denafrips Ares II
-Focusrite Scarlett Solo Gen 3 (recording at 192 kHz sampling rate)
-ifi iPurifier3 Male USB-B
-Monoprice Monolith Audio USB Cable
-Monoprice Stage Right XLR Cable
Software used:
-Audacity to playback and record test tracks
-DeltaWave null audio comparator
Reference track used: 1 minute clip of Human Nature by Michael Jackson (My personal CD rip, 16 bit/44.1 kHz .wav, lossless)
Test tracks were recorded using left channel only @ 16 bit/192 kHz to minimize sampling rate related errors
Notes taken before and after testing:
--------------------------------------------
ifi iPurifier3 audibility
-Record test track in Audacity
-Compare tracks using DeltaWave
-Control test usb cable against itself; control test iP3 against itself
-Take average of tests if run to run variations
-Test iPurifier with different PCs? determine if source PC causes changes
-Test 1: No iP3
-Test 2: iP3
-Test 3: iP3 vs no iP3
Results
-Ares ii very sensitive to vibration (may be audible)
-Focusrite ADC recording error (inaudible)
-run to run variations
-micro vibrations in DAC
-focusrite ADC error
-Results inconclusive
-too many sources of error
-Blind listening test may be only appropriate test
-Waveform deltas in both cases are channel crosstalk
-confirmed by playing back delta track
------------------------------------------------
Results and Discussion:

While recording the output from the Ares II I noticed that there were (what I thought to be random) noise spikes occuring in the right channel. The right channel of the DAC was not being recorded by Audacity. This noise turned out to be vibrations coming from the chassis of the Ares II. I found the source of the noise by accidentally hitting my desk while recording. I then tapped on various parts of the recording chain until I found what was causing it. The only noise that could be recorded was when I tapped on the top of the Ares II or hit my desk. Due to this finding, I can't ensure the integrity of the results.
Regardless, I will share my thoughts about the results that were obtained. Comparing the control tests (two tracks recorded using identical configarations) showed that there was measurable variation from one run to another. This variation however does not appear to be significant enough to cause DeltaWave to flag it (See image 2 iP3 control test).
iP3 control test.png
Keeping that in mind, when looking at the variables test in DeltaWave, there appears to be more of a difference between the control tests than there is between the variables (See image 3 iP3 vs none).
iP3 vs no iP3.png

Based on this result I can say: 1. The iP3 has caused a measurable change in the clock drift and jitter, but not for the better 2. Environmental noise (vibrations) caused more significant change than using the iP3, 3. Based upon the fact that I could not hear the recorded noise caused by vibrations, the iP3 makes no audible difference. I will point out that these results are only valid using the Denafrips Ares II. If you were to use a DAC that is more susceptible to USB issues you may have different results.
Post-testing I attempted to recreate the vibration induced noise in a new instance of Audacity but it was no longer there.

Extra pictures included show differences between Test 1-3 in DeltaWave.
 

Attachments

  • iP3 vs none clock drift.png
    iP3 vs none clock drift.png
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  • iP3 vs none linearity.png
    iP3 vs none linearity.png
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  • iP3 vs none spectrum compare.png
    iP3 vs none spectrum compare.png
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  • no iP3 clock drift.png
    no iP3 clock drift.png
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  • no iP3 control test.png
    no iP3 control test.png
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  • no iP3 linearity.png
    no iP3 linearity.png
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  • no iP3 spectrum compare.png
    no iP3 spectrum compare.png
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