Smartphone Audio Quality Testing
by Chris Heinonen on December 8, 2013 5:15 PM EST- Posted in
- Smartphones
- Audio
- Mobile
- Tablets
- Testing
In many of the examples you have seen so far, you notice that the Nexus 5 has a large issue with the left channel at peak volume levels. As Brian mentions in his Nexus 5 review, it is based on a similar platform to the LG G2 but it isn't identical. Because there are similarities I want to test it out and see if it has the same issue that I see on the Nexus 5.
The test that is causing the large issue on the Nexus 5 is a 1 kHz sine wave, at -0dBFS, at maximum volume. This is the loudest sound that any device will be asked to produce. If you're familiar with the trends in music mixing the past two decades you'll know that a peak of -0dBFS is not all that uncommon now. This chart at NPR shows the average and peak levels for the most popular songs over the past thirty years. Two decades ago testing for -0dBFS might not have been important but it is now. So lets look at this image from the Nexus 5 again.
Now for comparison, we will look at the LG G2.
This looks much better. However the LG G2 is still putting out 0.546528% THD+N into the left channel while only outputting 0.003338% into the right channel. So there is still some imbalance going on here. So why is the issue so much less on the G2 than on the Nexus 5?
The key to this is looking at the scale on the graphs here. While the Nexus 5 peaks are up close to 1.3-1.4V, the G2 has peaks that don't even reach 700mV. Looking at the actual numbers the G2 has a Vrms level of 475.3 mVrms while the Nexus 5 checks in at 843.6 mVrms for the left channel and 982 mVrms for the right channel. The G2 is placing far less stress on its headphone amplifier and keeping it from the output levels that cause this excessive clipping in the Nexus 5.
To look in more detail, we have THD+N Ratio charts for the stepped level sweep that we looked at earlier. First, lets look at the Nexus 5.
We see that the first three volume levels, 15-13, have THD+N distortion over 0.3% for the left ear, while they are below 0.01% for the right ear. From level 12 and below the THD+N levels are practically equal. Now to see how this data on the G2 looks.
We see the first volume step has 0.55% THD+N or so for the left ear, but the right ear is down at a similar level to level 14 on the Nexus 5. The next step drops it to 0.03% which is way, way below where it is on the Nexus 5 at that point. By step 13 they are equal.
The conclusion I pull from this is that both the G2 and the Nexus 5 have the exact same flaw right now. However, the G2 has attempted to hide it by reducing the maximum output level of their headphone amplifier. The Nexus 5 can play louder, but only with far more distortion. Given this I would expect there to be an update to the Nexus 5 at some point that lowers the maximum headphone level to something closer to the G2.
However this doesn't mean that the Nexus 5 is certainly worse to use with headphones. The top 3 settings are ones I would avoid due to the left channel issue, but I might avoid the top 1-2 settings on the G2 as well. If we consider 1% THD+N to be the maximum allowable level, that leaves 8 volume steps on the Nexus 5 that are usable. The G2 has 9 steps that are available to you, and 10 if you consider 0.03% THD+N in one ear to be OK (it probably is).
In the end, the G2 won't play as loud as the Nexus 5 will, but you don't want to play that loud anyway. It has more usable volume steps than the Nexus 5, and otherwise very similar numbers. I'll be interested to see if either of them make further changes to their maximum output levels to remove this issue.
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Impulses - Monday, December 9, 2013 - link
If I didn't say this on one of my previous comments I'll say it now, thanks for doing this! Audio quality is far too often ignored, specially amongst the PC/tech enthusiast crowd... And it's rarely tested very objectively when it's talked about at all.I wouldn't mind some subjective impressions atop the objective testing though... Or even some more commentary on Chris' part regarding the data itself. Knowing the Nexus 5 is clipping at max volume is one thing, but the reader might not necessarily realize it's not an issue at lower volume levels etc.
UpSpin - Monday, December 9, 2013 - link
Great review, I'm looking forward to further tests.A few suggestions:
- Such graphs are nice for a detailed analysis but useless for an easy comparison between different smartphones. Find a way to break down the important information in those graphs to one or two numbers, which you then list in a bar diagram to allow a comparison across different devices.
- As you pointed out yourself and also other commenters, testing THD at the max. volume might be industry standard, but it's useless for a normal consumer, especially, again, in such a comparison. As in the display tests where Anandtech adjusts to a fixed display brightness across all devices, you should do the same here. Because different headphones require different volume settings you might chose three settings:
A really silent one (fixed dB), a normal one (fixed dB), and the loudest possible (max. power the device offers).
For example on my HTC Desire I use Sony in-ear ear-buds which I drive with the lowest volume setting possible, else it's simply too loud for me.
- Those three volumes also have the advantage to go in detail in specific areas:
The loudest volume setting can be used to determine how much load the smartphone can drive and the consequences (just what you did with the Nexus 5, excellent).
The normal volume setting is a measurement for overall audio quality across all devices, because that's the one most people will use. So there a focus should be kept on dynamic range, frequency response, distortion, ...
The silent setting is to determine in detail the background noise. On my HTC Desire noise is audible with the Sony in-ear ear-buds (not with lower end normal ones). And as you said, if the device can output a lot of power, naturally the noise to signal ratio becomes smaller. But that's artificial and a useless measurement when compared to other devices. So keep the volume at a uniform low setting and measure the noise to get comparable and meaningful results across all devices. Also make sure to include some noise measurement while in Airplane mode and while transfering some data over mobile. Then you can judge how well the analog part was designed.
Impulses - Monday, December 9, 2013 - link
Problem is, the dB values Chris would use would often not correspond with the same volume (and power output) level you'd use, because you're using different headphones with different sensitivities. Settling on different power levels might be more correct but it'd probably leave a lot of people scratching their heads... It might be worth taking a looksee at the way Tyll @ InnerFidelity tests amps and headphones. He's been doing objective tests for quite a while and has found a pretty good balance as far as how to present the data in an easy to digest manner.stepz - Monday, December 9, 2013 - link
Having a couple different fixed power output comparison points should make not matching your exact listening volume less of an issue. At least it's a less arbitrary measurement point than the point where the manufacturer decided to put a virtual stopper on the volume knob. The fact that max volume clips with a specific set of headphones shouldn't matter too much. If the headphone amp is clipping due to limited current available then using higher impedance headphones may be able to use that volume level without clipping. And if aren't able to use it, just don't crank it up that high and problem solved.supergex - Monday, December 9, 2013 - link
Finally I waiting for this for years.Simple and probably stupid question, will you include Windows Phone smartphone?
Many thanks in advance for these tests.
Osamede - Monday, December 9, 2013 - link
Is this novel - or just getting up to par? From what I recall, GSMArena and Mobile-Review have been doing detailed measurement of phone audio performance for years.tom5 - Monday, December 9, 2013 - link
I had the HTC One and it played much louder than the G2 without distortions on the same headphones. HTC One is in many ways ahead of newer phones like the G2 or Z1.eio - Monday, December 9, 2013 - link
Bravo! you guys always set the standard of a proper product review.eio - Monday, December 9, 2013 - link
It would be even more great if interference can be benchmarked, like the noise of I/O, communication while playing a quiet music.panda-fu - Monday, December 9, 2013 - link
This is a step in a good direction!However, I don't think the "issue" with the Nexus 5 was explained properly. What is happening is that the volume control on the Nexus goes high enough that it's possible for the amplifier to run out of power against the specific load. This is perfectly normal, and the practical implication is that the maximum power of that headphone amplifier is lower than your published measurements - the result should be at <1% THD.
Also, all results should list the load against which they were measured. If you allow massive amounts of distortion and don't specify a load, it would be easy enough to claim that a 100W <1% THD into 8 Ohms rated amplifier is "discovered to be able to produce 1000W" - just as long as you disregard it being driven into a 2 Ohm load with over 50% THD.
A metric that might also be of use, and practical in predicting a headphone amplifier's real-world performance, is output impedance. Smartphones and tablets are usually used with low impedance, sensitive headphones, and if the output impedance is relatively high, it can affect real-world frequency response massively - sometimes similar in scale as the EQ you pointed out in one of the measurements. Of course, providing measurements made against a range of headphones with different impedance characteristics, as you seem to intend to do, will point at the same issue if there is any. But in that case, please provide impedance curves of the reference headphones.