Pixel USB-C Audio out measurements (Stepped sine tests added 1/24))

bjrmd · Oct 20, 2017

Important update 11/9/18:
Android Pie seems to have fixed the digital gain defaulting to max. This means that the stock implementation is now optimal and using the gain control app is not needed (unless you want more voltage from a Dragonfly Red).
This was not announced anywhere to my knowledge, but is very pleasant surprise. I found it accidentally while testing the new dongle (above link).
Updated: Edit--I did some further tests and unfortunately the gain optimization only seems to work with line in mode, not with a "forced" headset scenario. So with a headset inserted, the distortion bands are still present.
As of the Nov patch, Pie on the Pixel has fixed both the line out and headset mode distortion banding when using the Google DAC.
When looking at the tracings, assume that stock will look as good as the optimized.

Made a simple spreadsheet with data so far:

y4mJvN_YZxULEAyQXl85QcbqPP91lMpcinGzjKukDV0iEQM2JSD8oO9Z5Jraf2Fa1kX7rADKKjyzE7YE7O_SGiRL11dsXQY-x_UV0TLS2IkTZDUu6O5_nea0-aHY_J-f3f_2wNpYzGV3PxodWOYl4G4sYpWNarmwetwn_jJmri0HB4_2pS1VW4mbIC-DgB9RpYbP-9cVRtxB23xEiXv-91wOg

The above numbers are using my gain control app, android volume at 25/25 to produce the best possible output signal
Note, the voltage at distortion threshold is the point where harmonic banding becomes >5 dB.
The THD is the harmonic distortion at 250 mV, this would be about 90 dB using full size cans like the Senn 650/800 that have a sensitivity of 103 dB/V.

Will work on uploading the exact images if anyone is interested.

Stepped sine tests at higher output (750mV) - An attempt to see how high impedance, lower sensitivity full size cans will effect distortion.

Edit: I updated the measurements and comments

Edit: Tested Apple USB C Dac

Edit: Tested the HTC dongle

Edit: Tested the Razer Dac

Edit: Tested the Realtec Dac

Edit: Tested the Geekria Dac

Edit: Tested the Audiolab USB device

Edit: Brief test of Dragonfly red. I would consider this to be the gold standard, very low impedance (<.1), minimal crosstalk, high volt out (not on stock), very low distortion.

Edit: There appears to be 3 (at least) "modes" that the Google dongle will do. Depending on the impedance of the headset/line out device attached, the output voltage varies quite a bit.

Low impedance - .36 Volt (high efficiency iem's)
High impedance - .9 Volt (full size headphones)
Very high impedance- 1.8 Volt (line out)

What gets interesting is the effects on testing. The "reference" sites like GSMarena, are testing with a Y cable setup (as I was) and will see high voltage out even with headphones attached since the use case was taken from the line out initially. What made me aware of this was that my app was not reading the Spl correctly, as if the max voltage was about 7 dB down (which it was). Also of note, the reduction in output is not due to a change in the Dac digital gain (the one that adjust from 1 to 175), so the distortion bands are just as bad since they kept that gain at 175.

RMAA:
Used both a Senn 800S and Shure 846 as load, as well as no load.
Note the flat FR on the SE 846 which verifies the low impedance above.

So superb impedance, great voltage out, pretty good crosstalk (with low impedance iems).

But, significant distortion using stock gain settings:

And it has 25 volume steps (each tick is 2.3 dB).

r47z · Oct 20, 2017

going to subscribe for those that have invested in 3.5mm portable audiophile amps/iems.

audioman42 · Oct 20, 2017

Nice work. Subscribed!

By the way, very nice headphones. I'm looking forward to testing out LDAC on my MDR-1000Xs when my Pixel arrives.

Jooosty · Oct 20, 2017

Hi bjmrd,

So I was looking at the Phone arena review in regards to the audio quality through the dongle.

It showed this

Not sure if this means the 2XL is weaker than the 2?

What does your test conclude? Would this device provide a nice audio experience for the user ?

This is important to me as I use 3.5mm headphones.

Thanks in advance,

Previous devices are the V20 (superb) and the non DAC G6.

bjrmd · Oct 20, 2017

I double checked my voltage measurements and they seem correct (compared to a dragonfly red).
The dongle may contain a DAC (like apple lightening). It is possible that with root, ALSA, some of the distortion can be reduced if so. Certainly the voltage is good, impedance great.

Oh and each volume tick is about 2.5 dB.

Addendum - The dongle definitely has a DAC
I have ordered a USB audio pass through cable to see if onboard analog is enabled

jawmail1 · Oct 20, 2017

bjrmd said:
I double checked my voltage measurements and they seem correct (compared to a dragonfly red).
The dongle may contain a DAC (like apple lightening). It is possible that with root, ALSA, some of the distortion can be reduced if so. Certainly the voltage is good, impedance great.

Oh and each volume tick is about 2.5 dB.

Addendum - The dongle definitely has a DAC
I have ordered a USB audio pass through cable to see if onboard analog is enabled

bjrmd when you have a minute can you explain some of the numbers and what they might mean to the layperson. Why is high voltage good and low impedance good.

bjrmd · Oct 20, 2017

jawmail1 said:
bjrmd when you have a minute can you explain some of the numbers and what they might mean to the layperson. Why is high voltage good and low impedance good.

The max voltage is what limits the overall volume, so if you are driving over the ear cans and need power, this is helpful. Not important for sensitive iem's.

Crosstalk--a mixing of the R and L channels- not intentional. Better crosstalk--more stereo separation.

Impedance- internal resistance of the amplifier--if this is too high, causes frequency response changes depending on the type of iem and the iem impedance.

Jooosty · Oct 20, 2017

Thanks for the definitions bjrmd!

bjrmd · Oct 20, 2017

A couple of key points:

The dongle is a USB DAC, so basically audio out as supplied by Google is determined by that cheap little item. You could get a better USB DAC like a dragonfly, but it is bigger.

The distortion is based on some sort of driver parameter issue. I think the reason will end up being that the dongle DAC is set for max digital gain which is not optimal (unless needed). The following test shows why:

I used the Dongle on my Pixel orig and Pixel 2 with the Neutron player usb driver and the signal was clean.
This is a tracing, the same on both devices.

This is a dragonfly red, virtually the same:

So, I think the Google designers did not properly design the software, but the hardware is solid. In the meantime, use the Neutron player USB driver and you will have a very clean signal.

jawmail · Oct 20, 2017

bjrmd said:
The max voltage is what limits the overall volume, so if you are driving over the ear cans and need power, this is helpful. Not important for sensitive iem's.

Crosstalk--a mixing of the R and L channels- not intentional. Better crosstalk--more stereo separation.

Impedance- internal resistance of the amplifier--if this is too high, causes frequency response changes depending on the type of iem and the iem impedance.

Thanks:good:

bjrmd · Oct 21, 2017

Dongle optimization on the old Pixel:

Alsa installed (need root, so can't do on the new Pixel yet).
Dongle card output:

It seems that the android software defaults the dongle digital gain at max:

This leads to the distortion bands previously seen.

But, if we cut the dongle DAC gain down, and raise the android Volume to net the same(or even a bit higher) voltage:

The bands are gone.

In addition we can get 1 volt out without too much distortion as well:

This is not that difficult to do, but root is needed.
I will try to do some more detailed testing over the weekend, but I wanted to get this up so if someone was on the fence due to audio issues, if you are willing to wait for root and a few mods, this is a reasonable solution.

BTW for 9 bucks the dongle is pretty good with the correct gain settings

yangyangyanglei · Oct 21, 2017

do you have test the ldac on google pixel 2 xl ?
is it working? or any change?

Nitemare3219 · Oct 21, 2017

Does anyone else think it's a bit ridiculous how large the adapter is? It's huge compared to Apple's.

Thanks for posting this! Would you say this adapter is superior to Apple's lightning adapter? There are a few audiophile sites that have posted measurements for it and say it's great, but I'm not sure how to compare it to this.

Here is one such review: http://www.kenrockwell.com/apple/lightning-adapter-audio-quality.htm

bjrmd · Oct 21, 2017

yangyangyanglei said:
do you have test the ldac on google pixel 2 xl ?
is it working? or any change?

See first post.

In order to get digital gain to change in the dongle Dac, root is needed, hence tested the dongle on original Pixel in post 11.
The results should be identical .

bjrmd · Oct 21, 2017

Nitemare3219 said:
Does anyone else think it's a bit ridiculous how large the adapter is? It's huge compared to Apple's.

Thanks for posting this! Would you say this adapter is superior to Apple's lightning adapter? There are a few audiophile sites that have posted measurements for it and say it's great, but I'm not sure how to compare it to this.

Here is one such review: http://www.kenrockwell.com/apple/lightning-adapter-audio-quality.htm

The dongle is a reasonable USB DAC, but the stock implementation (at least on my setup) is poor. Google has the DAC digital gain at max, which introduces significant distortion.

To backtrack, the net powerout of this device is dependent on the Android system volume + the digital gain of the DAC itself. So you could have a very low android volume and very high DAC gain (as it is now) or a higher android volume and lower DAC gain (optimal for distortion).
My dragonfly red will behave this way as well in regards to distortion.
So unless you want maximum power out, we want android volume higher and DAC gain lower.

The impedance is lower than Apple's, power out may be higher as well. Not sure about crosstalk but both are probably very good.

Size wise- I couldn't even tell there was circuitry in the dongle-they did a good job IMO in the size.

Bottom line-- the audio out of the new Pixel is basically dependent on what USB DAC used. The stock is fine with the above noted. In fact for all you know, another USB DAC may also default to max gain and distort as well.

Nitemare3219 · Oct 21, 2017

bjrmd said:
The dongle is a reasonable USB DAC, but the stock implementation (at least on my setup) is poor. Google has the DAC digital gain at max, which introduces significant distortion.

To backtrack, the net powerout of this device is dependent on the Android system volume + the digital gain of the DAC itself. So you could have a very low android volume and very high DAC gain (as it is now) or a higher android volume and lower DAC gain (optimal for distortion).
My dragonfly red will behave this way as well in regards to distortion.
So unless you want maximum power out, we want android volume higher and DAC gain lower.

The impedance is lower than Apple's, power out may be higher as well. Not sure about crosstalk but both are probably very good.

Size wise- I couldn't even tell there was circuitry in the dongle-they did a good job IMO in the size.

Bottom line-- the audio out of the new Pixel is basically dependent on what USB DAC used. The stock is fine with the above noted. In fact for all you know, another USB DAC may also default to max gain and distort as well.

Here's the size comparison.

Jayme Helgerud · Oct 22, 2017

bjrmd said:
I double checked my voltage measurements and they seem correct (compared to a dragonfly red).
The dongle may contain a DAC (like apple lightening). It is possible that with root, ALSA, some of the distortion can be reduced if so. Certainly the voltage is good, impedance great.

Oh and each volume tick is about 2.5 dB.

Addendum - The dongle definitely has a DAC
I have ordered a USB audio pass through cable to see if onboard analog is enabled

Can you post a link of the pass through cable you are using or reccommend?

---------- Post added at 01:57 AM ---------- Previous post was at 01:50 AM ----------

I may be misunderstanding the tech involved here but what is the best way to get the best wired audio here? Root tweaking the existing dongle DAC or doing something like a pixel rooted with viper4audio with a pass through dongle?

bjrmd · Oct 22, 2017

Jayme Helgerud said:
Can you post a link of the pass through cable you are using or reccommend?

I may be misunderstanding the tech involved here but what is the best way to get the best wired audio here? Root tweaking the existing dongle DAC or doing something like a pixel rooted with viper4audio with a pass through dongle?

A pass through cable would be using the phones DAC/SOC (qualcomm) and analog audio out, just like with a headset jack. Unfortunately, @chdloc did a brief test with a Pixel 2 (not XL) with that type of cable and it did not play. Also, I bet the analog out would have higher impedance , worse crosstalk than a USB device. Either way you need an adapter, so a dongle or pass through.

So far the only way to get wired audio is through using a USB DAC. The dongle is a full fledged USB DAC. It has a fixed sample rate of 48K but otherwise excellent specs(by itself). Even if you wanted a high sample rate DAC, the android driver/audioflinger only puts out 48K.
As mentioned above, the stock gain settings cause distortion (at least in my case). After rooting this will be easy to fix. Right now, Neutron player has a custom USB driver that prevents that distortion (by also keeping the DAC gain lower) - that is what I am using.

Maybe Google will read this and fix the issue in the next update.

I can't give an opinion on Viper.

Jayme Helgerud · Oct 22, 2017

bjrmd said:
A pass through cable would be using the phones DAC/SOC (qualcomm) and analog audio out, just like with a headset jack. Unfortunately, @chdloc did a brief test with a Pixel 2 (not XL) with that type of cable and it did not play. Also, I bet the analog out would have higher impedance , worse crosstalk than a USB device. Either way you need an adapter, so a dongle or pass through.

So far the only way to get wired audio is through using a USB DAC. The dongle is a full fledged USB DAC. It has a fixed sample rate of 48K but otherwise excellent specs(by itself). Even if you wanted a high sample rate DAC, the android driver/audioflinger only puts out 48K.
As mentioned above, the stock gain settings cause distortion (at least in my case). After rooting this will be easy to fix. Right now, Neutron player has a custom USB driver that prevents that distortion (by also keeping the DAC gain lower) - that is what I am using.

Maybe Google will read this and fix the issue in the next update.

I can't give an opinion on Viper.

Will the neutron driver affect music played with other apps? I assume not...only music you've downloaded and are playing in the neutron app. It sounds like (haha) I'm going to be looking forward to some system level driver mods someone (hopefully) develops for a rooted pixel. Thanks for the insights!

bjrmd · Oct 22, 2017

Jayme Helgerud said:
Will the neutron driver affect music played with other apps? I assume not...only music you've downloaded and are playing in the neutron app. It sounds like (haha) I'm going to be looking forward to some system level driver mods someone (hopefully) develops for a rooted pixel. Thanks for the insights!

Sorry, no - only works in Neutron player.
Once root comes I plan on making something like this but will be much easier since only USB audio needs control. I would like some type of Spl level info as well to save our ears.