The RMAA (RightMark Audio Analyzer) Source and Audio Device Measurement Thread [Overview of Measurements in Post #3, Tutorial in Post #2]
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HiFiChris

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Very interesting. Focused FiiO Q1 MkII because of its price together with digitalised volume control, dac/amp + amp capabilities, and balanced output chance (i don't own any balanced gear yet).
pity its output impedance is over 1ohm (not too high though) and balanced hissing.
Thanks!!
Yeah, it could also be lower for my very personal standards that prefer 0.5 Ohms and below - but it' not that 1.2/1.3 Ohms are a high number at all, and while my inner output impedance perfectionist is slightly paranoid seeing that, my common sense tells me that it's still a value that is a good bit lower than what other devices have in terms of OI.

Most multi-BA models that aren't as much diva-like as the Triple-Fi 10 shouldn't show much deviation from the unloaded measurement at all.
 
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yuriv

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Google USB-C audio adapter with USB-C to USB-A adapter and box.jpg

The Google USB-C to 3.5mm headphone adapter for the Pixel 2 and Pixel 2 XL used to be $20--a fair price, I thought, because it can do more than the Apple Lightning to 3.5 mm headphone adapter. For example, it works with MacOS and Windows 10 Creators Update with the default drivers. But after some backlash from the public, Google lowered the price to $9, the same as the Apple audio dongle.

Google USB-C audio adapter + USB-A adapter.jpg


Over at xda-developers, they already have RMAA measurements when running it from Android. This post is about how it does in Windows, which shouldn’t be that much different.

When you plug the adapter into a PC, Windows doesn’t show it in its list of audio devices until something is plugged into the 3.5mm jack. If it’s a very high impedance load, Windows will say that it’s a line out. I measured 1.88 Vrms for a full-scale 1 kHz sine wave, which is the same as for the unit measured over at xda-developers. That’s a good 5.5 dB more than the Apple adapter’s maximum voltage. With Windows volume at 100, there’s how the line out did in RMAA:

Google USB-C audio adapter - line out RMAA summary.PNG

Test results from left to right: 1644, 2444, 2448, 2496

Google USB-C audio adapter, line out - 16 vs 24 bit 2444 noise.PNG

Relative noise level, 1644 and 2444


Google USB-C audio adapter, line out - 16 vs 24 bit 2444 DR.PNG

Dynamic range, 1644 and 2444


Google USB-C audio adapter, line out - 16 vs 24 bit 2444 1k THD.PNG

1 kHz THD, 1644 and 2444


Google USB-C audio adapter, line out - 16 vs 24 bit 2444 IMD.PNG

SMPTE IMD, 1644 and 2444

Google USB-C audio adapter, line out - 16 vs 24 bit 2444 stereo crosstalk.PNG

Stereo crosstalk, 1644 and 2444


fr.png

The frequency response in Windows 10 Creators Update seems to be limited: RMAA 2496 frequency response measurement shown.


The adapter doesn’t switch from line out mode to headphone out mode until the 3.5mm plug is disconnected from the adapter’s jack. It’s possible to get the higher voltage mode for a headphone with these steps: plug in something like a splitter or a 3.5mm to 6.3mm adapter with no headphones attached; the adapter sees an open circuit so switches to line out mode. Then plug in the headphones into the splitter or adapter. The device stays in line out mode. This could be useful for high impedance headphones like an HD600:

Google USB-C audio adapter <-- headphone splitter or 6.3mm adapter​

This switches it to line out mode (max. 1.88 Vrms). Then plug in the headphones, for example:

Google USB-C audio adapter <-- headphone splitter or 6.3mm adapter <-- HD600​

--------------------------

When the adapter is plugged into the PC and it sees a lower-impedance load, it switches to headphone out mode. Here’s how I determined the maximum voltage available:

Google USB-C audio adapter <-- headphone splitter <-- 16-ohm dummy load or earphones​

This switches the adapter to headphone out mode. When the dummy load is unplugged, it stays in headphone out mode. It doesn’t switch to a line out. I measured around 400 mV open-circuit voltage in headphone out mode this way. At xda-developers, they got two different headphone out modes, with different voltages. I didn't test to see if a third level was available in Windows or MacOS.

Here’s how the adapter performed with the 16-ohm dummy load:

Google USB-C 2444 into 16 ohms RMAA summary.PNG

Headphone out mode RMAA test results at Windows volume 100 (left) and 68 (right)


Google USB-C 2444 into 16 ohms RMAA frequency response.PNG

Frequency response: Headphone out mode into 16 ohms vs Line out mode


Google USB-C 2444 into 16 ohms RMAA noise level and dynamic range.PNG

Relative noise level and dynamic range: Headphone out mode into 16 ohms vs Line out mode


Google USB-C 2444 into 16 ohms RMAA 1k THD.PNG

1k THD into 16 ohms at Windows volume 100 and 68.

For me, comfortable listening level with most dynamic-driver IEMs doesn't exceed Windows volume 60. It's usually closer to 50.


Impulse response.png

Impulse response


High gain, max volume, no load.png

Line out mode, no load, Windows volume 100


High gain, max volume, 16-ohm load on both channels.png

Line out mode, 16-ohm load on both channels, Windows volume 100



High gain, Windows volume at 70, 16-ohm load on both channels.png

Line out mode, 16-ohm load on both channels, Windows volume 70



High gain, Windows volume at 68-2, 16-ohm load on both channels.png

Line out mode, 16-ohm load on both channels, Windows volume 68, onset of clipping


High gain, Windows volume at 66, 16-ohm load on both channels.png

Line out mode, 16-ohm load on both channels, Windows volume 66



Low gain, max volume, no load 2.png
Low gain, max volume, 16-ohm load on both channels.png

Headphone out mode, Windows volume 100: no load (left), 16-ohm load on both channels (right)


See also 407 * 16.2/(R + 16.2) = 393



16-bit J-test.png
16-bit J-test signal


24-bit J-test.png

24-bit J-test signal


I may have to double-check the J-test results.



My subjective take on the noise level with a UE600: It’s a very soft background hiss. It doesn’t produce irregular-sounding noises like an iPhone 6S does. At least not when moving around windows or when the SSD is busy.

So far, this Google adapter has outperformed the built-in audio of every computer that will recognize it. I tried it with a 2016 Lenovo Carbon X1, a few Microsoft Surface tablets, and a Chuwi mini PC. Macs usually have clean audio, but they can’t output 1.88 Vrms like this adapter.

The headset mic input works well with my headphone measurement rigs and REW, both in Windows and MacOS. It also works with my 2013 Nexus 7, which doesn’t have great built-in audio:

Google USB-C audio adapter, Nexus 7 (2013), IEC711 clone, Etymotic ER4PT.jpg


Edit 12/20: The mic input has a significant amount of roll-off in the bass. I compared it to the Startech ICUSBAUDIO2D audio interface, and it's around 5-6 dB down at 20 Hz. It probably has a smaller coupling capacitor. So if you're planning to use this adapter in a measurement rig, you'll need to make a calibration curve for the mic/mic input system.

Sadly, I couldn’t get the adapter to work with my Amazon Fire tablets. Maybe a FireOS update will fix it in the future.

Edit 12/30: It works on the 2017 Fire 10 HD with Fire OS 5.6.0.0! Still no luck on the 2017 Fire HD 8 or the 2014 Fire HD 6, both also running Fire OS 5.6.0.0.
 
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castleofargh

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didn't know you had a QA400. ^_^ (I'm secretly jealous of anybody who owns a 400 or 401).
 
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HiFiChris

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@yuriv

You don't happen to have an output impedance spec for the adapter, do you?
 
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yuriv

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didn't know you had a QA400. ^_^ (I'm secretly jealous of anybody who owns a 400 or 401).
I've had it for a while. There was a photo of it when I posted the Apple Lightning audio dongle measurements. But I would have gone for the 401 if it were available at the time.


@yuriv

You don't happen to have an output impedance spec for the adapter, do you?
It's in the post. I guess the link to Wolfram Alpha is easy to miss: 407 * 16.2 / (R + 16.2) = 393

They're getting a lower figure over at xda-developers: 0.43 ohms. I'm more conservative and try to make it so that if I mess up the measurement, I err on the high side.
 
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Chord Electronics Mojo:

No Load:



Something that could be considered as a slight slow roll-off filter. Nothing wrong with that.


Triple.Fi 10:



Seems like the output impedance is higher in the upper and super treble than it is in the bass and mids.


Various Multi-BA IEMs:



Seems like the Mojo doesn't fully like low impedance multi-driver loads.


IE 800:




Various Full-Sized Headphones:




I unfortunately don't have the link to the test/article in a print anymore, but it had the measurement on hand and stated that while the output impedance was very low (I think measured at) 1 kHz, it was a bit higher at (I think measured at) 20 kHz.

The question is whether these more or less slight deviations do matter to you or not as most of them are above 10 kHz anyway, however objectively speaking, the Mojo could stay somewhat more linear in the treble with complex and low impedance multi-driver loads.

I read a statement from Chord Electronics some time ago that they designed "[...] Mojo['s] analogue section [...] very simple, so giving Mojo's transparency, but the downside is a small variation in frequency response with load impedance" (http://www.head-fi.org/t/784602/cho...d-please-read-the-3rd-post/4320#post_12058437).
I just saw this. This explains the response up top. Since it's not flat, it tells me there is a bit of a reactive load.

Chord_Mojo_Center_-_-_-_-_-_20-20k_-_impedance.png

Looking at the TF10 impedance response and the Mojo's impedance response, it's apparent why the response looks like that.

dd4041.png
 
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I just saw this. This explains the response up top. Since it's not flat, it tells me there is a bit of a reactive load.



Looking at the TF10 impedance response and the Mojo's impedance response, it's apparent why the response looks like that.

Yeah, I'm fully aware of that - the Mojo's output impedance starts climbing in the middle highs, hence this behaviour. It's good to finally see that on a publicly available measurement graph, since the one that I am already aware of and that also confirms an impedance rise in the highs is in a copyrighted print document that I cannot share for obvious reasons - thanks for posting!
 
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:L3000:
I just saw this. This explains the response up top. Since it's not flat, it tells me there is a bit of a reactive load.



Looking at the TF10 impedance response and the Mojo's impedance response, it's apparent why the response looks like that.

I would be curious to see Impedance curves of Hugo2 or Dave for comparison. Not yet found.. :L3000:
 
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:L3000:

I would be curious to see Impedance curves of Hugo2 or Dave for comparison. Not yet found.. :L3000:
We all know that headphone out impedance is not purely resistive, and can be reactive, particularly capacitive to roll off the low end significantly with a capped output, but this is the first I've seen of a source output impedance response, and paritcularly the top end impedance vary in impedance specifically. This goes to show how much we can see from source output impedance response.
 
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The deviation is only about 0.5dB, at worse it's about 1 dB a 10k I don't think it's significant enough to be noticeable
 
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castleofargh

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The deviation is only about 0.5dB, at worse it's about 1 dB a 10k I don't think it's significant enough to be noticeable
on one hand, it's obvious that it doesn't matter. picking any IEM over any other IEM will result in so much more changes. and just the way we place the IEM from one time to the next can generate a more significant variation in sound.
on the other hand, it's for a device where the designer talks about silly small stuff as if they were audibly significant. so by my standards it's irrelevant, by the typical Chord standard it's a disaster. ^_^
 
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If you level match speakers, you'll still get variations if you turn your head one way or the other too. There is such a thing as "close enough for government work".
 
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bartzky

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so by my standards it's irrelevant, by the typical Chord standard it's a disaster. ^_^
Interesting point of view :-D This made an interview with Watts come into my mind in which the talks about the huge benefits of 350 dB noise shaping performance...
 
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on the other hand, it's for a device where the designer talks about silly small stuff as if they were audibly significant. so by my standards it's irrelevant, by the typical Chord standard it's a disaster. ^_^
XD
by my hearing standards it's ok as well, but by multi-ba iem measuring standards, it made me search for another dac+amp source.. pissed off
 
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