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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porphyr - Monday, December 9, 2013 - link
This article is fantastic. I love that you are going to be testing audio quality. Obviously testing anything takes a lot of time, but I think it would be nice to see how these phones perform at "reasonable" listening levels. It would be great if you could pick dB level that is pleasant through the apple earpods and test a 2nd time at that, sort of how you use 200 nits for panel tests. That would give a more helpful representation of performance. Another thing that I would really appreciate is an explanation of how bad (or good) performance needs to be for most people to hear the difference (with bad and with good headphones). Thanks for the piece.99sport - Monday, December 9, 2013 - link
Thanks for the great article.Can you add built in speaker testing? I have an HTC one, and while I prefer to turn beats audio off when I use my phone in the car (listening to music on the car's speakers), I much prefer the sound of the built in speakers with beats audio on. As others have pointed out, all of the pieces in the chain are important to sound quality. My guess is that the frequency response of the built in speakers is much less at low frequency, and the beats audio increase in gain shown in your chart (below 100Hz) is designed to compensate for the frequency response characteristics of the built in speakers. In other words, if you tested the frequency response of the built in speakers (using a microphone with a known linear frequency response to gather the data), would the curve be much flatter when using the built in speakers with beats audio turned on versus turned off? Would the HTC one with beats audio on in fact have a much better (flatter) frequency response through the built in speakers than other phones do through their built in speakers?
It would be very useful to be able to compare the sound quality of the whole sound reproduction chain including the built in speakers – for me, the built in speaker sound quality and volume level is a major discriminator between phones – right up there with display color accuracy and camera quality.
dishayu - Monday, December 9, 2013 - link
Excellent initiative. The HTC One frequency response looks dreadful. I'm looking forward to graphs with beats enhancement off.As the next step, I would really like to see where different types of audio devices compare to each other... smartphones, ordinary media players (ipods), audiophile media players (HM-801), entry level/top level PC sound cards, realtek onboard chipsets.
NeoteriX - Monday, December 9, 2013 - link
I'm not sure if it's necessary to go through the effort of including PC soundcards, motherboard solutions, etc., but including media/MP3 players would definitely be a nice addition. The place that mobile phones have now as media consumption devices in addition to being phones came as an evolution from the original media device.However, the media device, given its singular purpose, prominently had sound quality as a major review component, and consumers did look at the DACs and opamps used. When they evolved to all-purpose smartphones, suddenly there were a lot of other features that took precedence, including processing power, display quality, etc.
Now that AnandTech is shepherding in a new look at audio quality, comparing the state of mobile phones to the heyday of media device would definitely be useful.
stunta - Monday, December 9, 2013 - link
Excellent article! It would be fantastic to see results from commonly used mp3 players. iPod, Sandisk Sansa (Clip, Fuze etc.) etc.How do you feed the test tone into the phone? Does the Audio Precision device come with test files you simply drop on the phone and play?
Also, do we know if these phones use the same amplifier for the built-in speakers and headphone outputs?
Thanks again!
Impulses - Monday, December 9, 2013 - link
I'll second this and dishayu above, it'd be a great reference.Hell, if we could get you to test output of a few BT receivers out there that might also be interesting and valuable to readers... I know BT's another can of worms as it introduces more compression etc, but it's actually gotten quite decent and those receivers end up replicating (and thus bypassing) many of the same components in phones.
There's not a lot of in depth reviews out there for those things but seeing as you can use them with any pair of headphones they'd fit right into your testing and they can be a suitable solution/alternative to a phone's line out. Something like the older Sony MW-300, or the newer models, or three equivalent Samsung/LG models.
Panzerknacker - Monday, December 9, 2013 - link
Please test the Oppo Find 5! I use that phone and it should have good audio capability. Wonder how it does vs iPhone 5.juhatus - Monday, December 9, 2013 - link
Now if only apple would enable their audio tech (noise-cancel atleast) on bluetooth.I downgraded from nokia 800 to iphone5 and atleast using the in-car-bluetooth the audio on calls went really bad.
On other comment, the graphs are huge in this article, maybe little scaling or something? some bare flatlines there and very big size graphs.
Nice article :)
Impulses - Monday, December 9, 2013 - link
Great article, though I have a quibble with the headphones to be used for future testing... Nothing against either as I've owned both, and the SR80 are a fine candidate (common entry level open headphone recommendation). The AKG have a reputation for being hard to drive and they aren't exactly very portable anyway, plus they represent another dynamic open headphone. I think a popular IEM (Ety, Shure, even Apple's dual driver IEM) might be a better second alternative, if it's at all possible with your rig... I know IEM are a pain to test due to seal issues and whatnot. Failing that maybe some other dynamic headphone that's more likely to be used with a mobile device (V-moda M-80? Senn HD25-1 II?), or something cheap yet extremely popular and good for the $ (Koss Portapro or KSC75).Impulses - Monday, December 9, 2013 - link
Also, if you could test and report output impedance for the phones that would be a HUGE help for people trying to figure out what kinda headphone would work best... Relatively high output Z isn't uncommon and it can wreck havoc with some lower impedance headphones, particularly sensitive IEM (and specially the multi balanced armature models that are so prevalent now).