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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Origin64 - Monday, December 9, 2013 - link
"Here we see that Beats is adding a +3.5 dB boost from 60 Hz to 90 Hz, but the deviation from 0 dB goes from 30Hz to 300 Hz. Past 6.5 kHz we also see a rise in the treble."And people pay 300 bucks for a headphone that does exactly, and only, this. Its a good joke, really.
willis936 - Monday, December 9, 2013 - link
To Chris:Check out NwAvGuy's blog if you haven't already. He appeared and disappeared a few years ago bringing with him a headphone amp design and (more importantly) a breath of fresh, objective air in testing audiophile headphone equipment. He has some good data there and comparing testing methodologies might be insightful for things to try here on anandtech.
cheinonen - Monday, December 9, 2013 - link
I've read his full blog and wish it was still updated.Impulses - Monday, December 9, 2013 - link
Tyll's Inner Fidelity blog is another great resource.adityanag - Monday, December 9, 2013 - link
This is excellent. Also the reason why I've been reading Anandtech since 1998. Keep up the great work, guys.Gadgety - Monday, December 9, 2013 - link
I appreciate this article, Chris. An improvement would be a summary table of all the models compared on one page, and some sort of analysis beyond the "poor performance" comparison. I've also seen data that the specs will change significantly for worse when headphones are attached to the phones.xodusgenesis - Monday, December 9, 2013 - link
Finally some in-depth audio anlysis. I've been waiting for this as I actually use my smartphone as a phone (I know shocker in today's age) and media player most of the time.ZoSo - Monday, December 9, 2013 - link
Would like to see some results of a few current WP8 phones, Nokia in particular.asgallant - Monday, December 9, 2013 - link
Awesome! I have been wanting to see some audio analysis done for a while now. Is there any chance of extending this to test audio on motherboards, sound cards, and laptops as well?lever_age - Monday, December 9, 2013 - link
Glad to see this. My suggestions are as follows:1. Include an output impedance measurement. If you're using these as decent-quality audio players with headphones, this is one of the most important things to know for certain headphones, at least. Who cares what the measured frequency response with a resistor is if your source's output impedance is causing +/- 5 dB swings in response for some balanced armature IEMs?
2. Standardize THD+N tests to a given output level for all phones (say 0.1 V or whatever else; the danger is picking something standard like 0 dBu that some phones could possibly not even reach). Don't just use whatever the max volume is, especially since that's into clipping territory for some phones. People don't scale their playback levels by how much power the electronics is capable of handling. I hope. Referencing a fixed level is more fair.
3. Please do keep reporting which phones run into clipping (and at what load) at volume settings at max or less. Also what some nonstandard settings like Beats Mode do.
4. Make careful distinction of THD with headphones as load and as not. If not loading with headphones-level impedance that is mostly testing the performance when hooked up to say a speaker system with a patch cable, which I don't think many people are doing these days.
5. When reporting maximum level, standardize to point of say 1% THD (or max volume, whichever comes first). Also note if headphones are used or not. It'd be meaningless to quote maximum levels far past the point of clipping.
6. If you have time, see if you can coax and measure some bad behavior out of the phone by using Wi-Fi, Bluetooth, LTE, etc. simultaneously, maybe some CPU/GPU load and seeing if that causes audio issues. Honestly, glitchy or cackling playback are far greater issues to audio quality than looking at 0.3 vs. 1 dB dips in frequency response at 19 kHz or something like that. Or output power levels most people don't need.