CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS
Lobby => Amp and DAC Measurements => Topic started by: Marvey on August 31, 2015, 05:21:56 AM
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Measurements for iFi iDSD Nano. My opinion of the sound quality of this as a DAC or DAC/headamp are elsewhere.
I set the volume to be within the the QA400's limits so the direct inputs of the QA400 could be used. The line outputs of the iFi were used, not the headamp outputs. The unit was acting funny so I updated the firmware. This time around, I used the differential probes on /10 and cranked up the volume all the way. The use of the probes increase the noise floor of the measuring equipment about 10db. 0dBr in the graphs was set represent the max output of the iFi. ARTA was used to generate the 16/44.1kHz signals from a PC to the iFi via USB and unfortunately DirectSound. Finally, my home is a noisy environment with lots of LED, CFB, dimmer, and Ethernet over A/C electronics. Right channel is displayed to get a sense of the limitations of the measurement equipment.- 1kHz @ -1dBr. The standard 1kHz measurement with the DAC running at almost max output.
- 1kHz @ -90dBr. Low level signal @ 1kHz vs. noise floor.
- 1kHz @ -1dBr. Same as above, but this time we are taking a close peak at the spectrum below 1kHz.
- 19kHz + 20kHz. IMD. Slighter wider band view.
- 19.1kHz. Wide band view.
- 700 and 1700Hz two tone. Log x-axis.
- massive multi-tone test.
- PN white noise. Wide band view to note extension and nature of filter slope.
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To be fair, this is a USB DAC. Getting power from USB is not necessarily the best way to go, but it does have portability advantages ("less wires" as my wife likes to say). Honestly, I thought something was totally wrong, until I checked the equipment really quickly with the Yggy and the Modi. I'll get Schiit Modi 1 (also a USB powered DAC) results tomorrow. The Modi 1 measurements are not great, but I already know they are not this undomesticated.
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(http://i.imgur.com/gspJiBy.jpg)
I'd elaborate but apparently it was deleted on head-fi and the 'mentions' of a certain Analog Devices chip were redacted by the poster whose product is measured here.
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But GO is awesome and is portable so no excuses really. Noise might be common mode crap if adc and dac share the same usb card/pc. Might not be the case with the Yggy due to awesome sauce usb but its an issue with usb powered DACs. I gave up on the Modi 1 because I thought I was measuring a broken device :X
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@oultrabaick:
iFi posted that AD5971 can't do 120db SNR due to glitching. And that PCM1793 was superior to AD5971 in terms of Spurious-Free Dynamic Range.
Frenchbat pointed out atomicbob's Schiit Yggdrasil Measurement showed >120db and ask ifi for reply.
About less than one hour of Frenchbat's posting, Ifi's original post got [redacted] and no mention of AD5971 anymore.
this was the post that got redacted:
http://www.head-fi.org/t/702376/ifi-audio-pro-desktop-line-discussion-thread/720#post_11864881
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@oultrabaick:
iFi posted that AD5971 can't do 120db SNR due to glitching. Spurious-Free Dynamic Range
The glitching thing is overblown. Unless iFi has been working with the chip, they really wouldn't know the exact nature of the glitching. Sure there are data sheets, but only certain case scenarios are covered. Also, there are ways to greatly mitigate the glitching. I read a paper on the Internet on how to address this in a very elegant way and it turned out that Schiit did exactly this. The hint is in the architecture.
In terms of spurious-free dynamic range, a huge part of this is power supply.
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There was some screwy behavior with this unit. I had to update the firmware before it even worked. Let me update it again and give it a try. I'll crank up the volume and use the diff probes and see what happens.
EDIT: Updated firmware. Redid all tests. The volume control works correctly with line out. Noise floor now looks right, revealing a few more things. Certainly much better looking measurements now.
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Well, that's a bit better the utter disaster in the original graphs.
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1) Early treble rolloff starting past 15kHz and -4db down at 20kHz. (graph #5)
2) -60db sidebands on IMD test. (#4)
3) Spikes in multiples of 60Hz below 1kHz @ 1dBr with rising noise floor as we go downwards in frequency. (#3)
4) Lots of junk in 19.1kHz test - out and inside of audio band.
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With the new FW ... does this change the subjective rating on the chart of awesomeness or does it still need to float ?
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Subjective rating the same. The better noise floor does reveal a bit more - not sure it did any favors. (Note, corrected last graph, the 19.1kHz test which was missing).
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Love the measurements. My new mantra for audio: "Measurements or it didn't happen."
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This is one of the units with selectable digital filters, yes? No?
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Yes, all measurements were done on standard filter.
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Wow, that much roll-off from the standard filter? That's special! Haha.
Found this as well for comparison: http://ifi-audio.com/audio_blog/does-the-nano-idsd-measure-good-bad-or-ugly/
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And the stop band attenuation is insufficient.
I'm no expert on this, but on the Soekris Dac this kind of stop-band is audibly shitty sounding. At least -110dB is needed, to my ears.
But then NOS (not true, pure nos though) was fine on it..
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Stop-band attenuation and slope ... based on personal preferences. The AGD M7 allows the user to change this. The higher stopband setting on the M7 had a denser sound, but grainier treble.
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So this ifi's Thorsten Loesch isn't as “Tonmeister” (“Soundmaster”) as he claims to be... basing on how bad the Ifi measurements are.
"To be allowed to charge money for my services as a sound engineer, I had to complete a part-time course (totalling nearly 2 years) after which I was able to call myself “Tonmeister” (“Soundmaster”)."
http://www.audiostream.com/content/qa-thorsten-loesch-amrifi#ZBblGiADpeKCvp76.97
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It's an inexpensive implementation running off of USB / battery power. I wouldn't expect it to have exemplary measurements. Subjectively the sound is nice, warm, and rolled and quite unoffensive (no digital glare, digitius, nasty treble, etc.). Maybe too inoffensive and forgiving for my tastes. Attacks and dynamics are soft. Microdynamic and microdetail is poor. What would be interesting is to compare measurements from DACs that sound differently.
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I added one more measurement to first page, 600Hz and 1700Hz two sine plotted on x-axis log.
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Added 17 tone test.
Redid all tests for best case scenario. Not sure what happened before (maybe USB power from laptop sucks, or battery not fully charged.) Measurements look much better now.
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I'm trying to wrap my head around the 17 tone test, seems very interesting. Have you discussed it already? 100/200/300/400 and roughly third octave spacing above that. It doesn't seem to be about looking at IM sidebands, since groups of tones are harmonically related. I'm assuming that the peaks are a straight line in the input signal, and we're supposed to be looking at the straightness of the peaks in the output signal, but I don't know. Can you provide some insight into this test and how you interpret it?
Cool stuff.
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I'm assuming that the peaks are a straight line in the input signal, and we're supposed to be looking at the straightness of the peaks in the output signal, but I don't know. Can you provide some insight into this test and how you interpret it?
I think that is one part of the information coming from the test. Also, you can compare the 17 tone to the 2 tone test and look at the noise generated when a DAC has to deal with a more complex load. I can definitely see the benefits of this test and currently cannot imagine any down-sides. Caveat is that I am still a noob in terms of the basics so I don't have the experience in looking for "gotchas".
EDIT: Just thought of some constructive critical questions:
Should the tops of the tones be linear? or Shouldn't harmonics be constructive interference?
Are the tones selected the "right" tones for the test? My knowledge of music theory is pretty low.
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The built in amp in this thing sounds like ass and really holds it back. As a DAC only it sounds OK.. but that really isn't its target function and one would be better served with a Modi 2U if you're hooking it up to another amp.