I’ve been playing most of today with new Sony HAP-S1 “HDD Audio Player System”. I’m planning on writing a full review soon but thus far I’ve been focusing on the Digital Sound Enhancement Engine or DSEE feature. If you missed yesterday’s post, I’d recommend reading that before continuing with today’s post. You can click here to access it.
I’m struggling with the whole concept of developing a feature that re-generates high frequency information that is lost when original CD quality tracks are compressed into MP3 files (typically at around 128 kbps…recall that CDs have a bandwidth of 1411 kbps). I guess there are so many casual music lovers out there that have vast catalogs of poor quality, heavily compressed audio files that will believe that they can restore them to “their original quality” that including DSEE in their new line of players is worth the investment.
Why not just go back to the “original quality” CD and import them into the new hardware? Then you really would get the real deal.
The online information about the DSEE process makes it sound pretty promising. I talked about the fact that MP3 compression does a lot more than just roll off some of the highest frequencies yesterday. I promise a post that will address the damage that can be done during the 10:1 data compression scheme that Fraunhofer came up with many years ago and which launched the downloadable music era.
So I thought it would be interesting to see how good the DSEE process actually is. By looking at the spectra of the files along the way, we should be able to see whether the DSEE process actually does restore an MP3 files back to its original fidelity.
So here’s what I did. I took one of my favorite high-resolution audio tracks, the “Mosaic” track of Laurence Juber, and converted it to standard CD resolution (44.1 kHz/16-bits) from the original 96 kHz/24-bit stereo master (I used the Sonic Process application set at steep and noise shaped…which maintains the highest amount of high frequency information). This is the track that is available on the FTP site. The SRC files are available on the site as well (I know I still have to talk about the various types of sample rate conversion etc). Then I took the CD res file and created an MP3 128 kbps stereo file, which I transferred to the HPA-S1’s HDD.
I captured the playback of the DSEE processed MP3 file into my Pro Tools rig at 44.1/16-bits and created spectragrams at every file involved. Take a look at Figure 1 below:
Figure 1 – The spectra of “Mosaic” in various formats [Click to enlarge].
So does the DSEE process restore the high frequency content that was absent from the MP3 file? No, clearly it does not but it does add some information at the very high end. Let’s take a close look at the plot.
The green line is the high resolution original file and looks wonderful all the way out to 48 kHz. The red line in the plot represents the CD version. The amplitude is several dB lower than the original (more on that in an upcoming post). As we expect, it stops at 22.050, the max for a compact disc. The light blue line is the MP3 file. It tails off at about 17.8 kHz but doesn’t really resemble the uncompressed version after around 16 kHz. Those high frequencies are data devils with regards to space…lots of information up there that isn’t going to get through your ear buds anyway.
The purple line is the DSEE processed output from the HPA-S1, which does departs from the MP3 file’s spectragram at exactly the same place…16 kHz or so. And you’ll notice it also has some spikes that don’t belong (please forgive the different amplitudes…I lowered the DSEE processed file so that it would be easier to see). The segment of the purple line above 16 kHz can be attributed to the DSEE process. We’re talking about 4 kHz of bandwidth that was removed from the original CD and “restored” by the DSEE process at much lower amplitude and with a completely new shape.
It’s your call on this one…is it worth having a processor try to “fix” the problems of the MP3 format (or any other heavily compressed audio file format)? You have three choices: go back to better sources and get definitive copies at real fidelity, live with the degradation of the MP3 format or turn on DSEE and get some made up high frequency information added to the highest range of the audio spectrum.