[Xperia Z2 General] sam_conrad:
Is there an issue with your Z2? :( That stinks.

I don't use the Walkman app or play MP3s. I use Spotify on their highest quality setting, which is a 320 kbps Ogg Vorbis file at near-lossless quality. Get ready for a long, detailed and technical response, though. :p

The DSEE HX audio function is designed to replace lost information in low bitrate MP3 and AAC files.

MP3 is the most common compression codec as well as one of the worst in efficiency, though many are moving away from it.

AAC files are the standard compression format for iTunes downloads, for example. It has somewhat better sound at the same bitrate as MP3.

Before getting too much into the technical talk, it's important to understand that during music compression, information is lost or distorted. It's very similar to same as JPEG compression-

[IMG="http://redstarwebdevelopment.com/wp-content/uploads/2011/10/jpg-compression1.jpg"]http://redstarwebdevelopment.com/wp-content/uploads/2011/10/jpg-compression1.jpg[/IMG]

Obviously, the compression saves lots of space but reduces quality of the image. Audio compression works in pretty much the same way. Where JPEG compression loses detail in fine lines and details, audio compression, especially MP3, loses lots and lots of high treble and can muddy and distort sounds from base to midrange especially with attack. You end up with loose sounding bass notes, and a sort of metallic-ringing with midrange sounds.

For example, here's a listening comparison.

64 kbps MP3 / AAC

http://nigelcoldwell.co.uk/audio/mp3vbr/abr064.mp3

http://nigelcoldwell.co.uk/audio/aacs/aac-064.m4a

128 kbps MP3

http://nigelcoldwell.co.uk/audio/mp3vbr/abr128.mp3

320 kbps OGG (lets pretend this is the lossless source file)

http://nigelcoldwell.co.uk/audio/oggs/ogg-09-11(320).ogg

Source: http://nigelcoldwell.co.uk/audio/

You can tell that the compressed files don't actually sound too bad, but if you pay attention, you'll notice the 64 kbps files sound kind of sloppy in general and in all three compressed files, the drum track at 20 seconds, and the following clip too, sound very deflated because they're lacking the treble extension of the high bitrate file. The whole idea of DSEE HX is to reclaim this treble extension and bring the frequency response of the file back closer to the original lossless file. To be honest, there isn't much Sony can do with the rest of the distortion. Once data is totally lost, or, say, disfigured, it's pretty much there to stay. Trying to fix all of this might seem like a good idea in theory, and it makes a nice selling point for their marketing team, but I don't think it really helps anything.

First off, if you can't hear the difference in the files, or say, maybe you can't hear a difference between the 64 kbps MP3 and 320 kbps OGG Vorbis files, or possibly, you don't even care, then it's probably not going to make your entire collection of low bitrate MP3s sound any better to you.

Second, if you can hear the difference in the files, and you prefer the high quality audio, DSEE HX is not going to magically make the 64 kbps MP3 sound anything like the high bitrate file. What the software is going to do, is essentially listen to your music playback and plot out a frequency response graph. It will then say, "Hey, I think this is compressed too much because there is almost no treble beyond 14 khz." ... it will then take the almost-no-treble and boost it to a level it thinks would be closer to a high bitrate file. This sounds nifty, but I'd say "it's trying to make something out of nothing". What's left of the treble extension that would normally be in a high bitrate file is usually left very quiet and very distorted in a low-bitrate MP3. You just end up with lots of harsh metallic grainy sounds because it's trying to boost the treble from ridiculously silent to audible again.

Plus, the issue compounds on itself. The more compression you've used, the more DSEE HX has to compensate (read then see the 128 kbps MP3 graph below, It has almost zero information above 16 kHz...), and the less it has to work with. If you've got an entire library of 192 kbps MP3s or 160 kbps OGG / AAC with less dramatic compression artifacts and information loss, maybe it will help reclaim a little, but that's subjective and the scenario is unlikely. TL;DR, So no, DSEE HX will not help.

Here are some visual graphs that also explain what happens -

These are basically heat graphs of the frequencies over the length of the song. Y axis is frequency, X axis is time (song playing, beginning to end). Deep red means there is a lot of that frequency playing, purple is a little bit, and black is nothing.

(Source: http://www.torrentech.org/index.php?act=Help&CODE=01&HID=56)

FLAC (I Feel You, Depeche Mode) 31.2 MB filesize

[IMG="FLAC (I Feel You, Depeche Mode) 31.2 MB filesize"]http://www.torrentech.org/collections/help/spectrals/flac.png[/IMG]

As you see here, treble extends up to 21 kHz and there is a gradual fade from bass to top end treble. This is normal and corresponds with the way the music was meant to be heard. Nobody wants to hear a constant and harsh drone of noises in the 16-22 kHz range, because that's unnatural. However, it's important that those are there because sounds that we hear are typically made up of many harmonic frequencies that blend together to give the sound of whatever object. Hi-hats are good examples of an instrument that sounds much different without treble even though most of the sound from them occurs in the midrange.

Here's a 128 kbps MP3 file of the same song -

LAME mp3 128 kbps (I Feel You, Depeche Mode) 4.3 MB filesize

[IMG="LAME mp3 128 kbps (I Feel You, Depeche Mode) 4.3 MB"]http://www.torrentech.org/collections/help/spectrals/mp3_128.png[/IMG]

As you can see, even at 128 kbps, you've already lost almost all treble extension above 16 kHz. This is a trademark "feature" of the MP3 codec. DSEE HX tries to reclaim what you saw from the FLAC graph from this graph. How well do you think that works? If you look closely too, you'll see the graphs don't even look the same in the midrange and bass range. There is distortion due to the compression. ;)

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Also-

The High Resolution Audio function in the sound settings, only upsamples the system audio from 44.1 (CD standard) / 48 kHz (DVD standard) sampling rate to 96 / 192 kHz. This is useless unless you have a dedicated USB headphone amp and your source files are something like lossless FLAC encoded at 96 kHz.