I wanted to continue the discussion that I started the other day (click here to read it) about algorithms that attempt to “restore” the sound of an MP3 back to their original “pre-encoded” fidelity. The initial analysis was performed on my “Mosaic” track encoded at 96 kbps. Today, I would like to show what happens when the same track is encoded at a higher rate…at 128, 256 or even the 320 kbps rate.
The Apple iTunes store (and most other digital music download stores) used 128 kbps as the standard bitrate for their music downloads. These days that rate has been pushed up to 256 kbps…so the likelihood that anyone is purchasing files at 96 or 128 is pretty slim. I just downloaded the “Happy” song by Pharrel Williams (I loved the “Despicable Me” movie and thought this tune was a perfect match for the story). It’s a typical overmastered, commercial hit with limited dynamic range (34 dB), but is a vast improvement on the days of 96 kbps.
So what does the Harman Kardon Clari-Fi technology do when presented with a 128 kbps MP3 version of “Mosaic”? Take a look:
Figure 1 – Spectrum of “Mosaic” encoded as an MP3 file at 128 kbps with and without Clari-Fi. [Click to enlarge]
There are a couple of notable points about this level of MP3 and the Clari-Fi process. The first is the lowering of the amplitude. It’s almost 5 dB quieter than the original MP3 file. I don’t know why this would happen. Perhaps the designers are concerned about some of the new frequencies exceeding the limit? The second thing is that while the high frequency slope of the plot is extended in the Clari-Fi example, there is a boost in the 5-12 kHz region that would “enhance” the sound. I’m not sure the addition of frequencies between 18 – 20 kHz is meaningful in this case. Listeners will most likely experience a difference due to the “equalization” differences.
Again, the process doesn’t address the most critical damage that lossy algorithms inflict…the removal of low level partials that are masked by the louder sounds.
Here’s the spectrum for the 256 kbps example:
Figure 2 – Spectra of “Mosaic” encoded as an MP3 file at 256 kbps with and without Clari-Fi. [Click to enlarge]
There was 3.6 dB attenuation as a result of the Clari-Fi process AND a noticeable bump in the level above 2 kHz compared to the original MP3. At 256 kbps the encoded file is very close to CD Quality. It would be hard to distinguish them apart with moderate equipment or using an iPod or other portable player.
Finally, here’s the same thing at 320 kbps…the highest MP3 encoding level available for commercially downloadable files.
Figure 2 – Spectra of “Mosaic” encoded as an MP3 file at 320 kbps with and without Clari-Fi. [Click to enlarge]
So the folks at Harman are doing more or less the same thing in this example…boosting the levels of the mid to high frequencies. At this point, there’s really no need to talk about the increased high-end…since the original 320 MP3 file can deliver CD Quality.
So are these techniques meaningful or just another sales/marketing slogan? They do make an audible difference…more at the 96 or 128 kbps bitrates than the higher ones…but once you get to 256 or 320, you’re almost at CD Quality anyways so why bother?
If I had my way HTC and Sprint would play up the appeal of lossless audio at 96 kHz/24-bits to serious music listeners and let the MP3 crowd enjoy the great in-ear phones or powerful speakers on the front of the M8 phone. Clari-Fi is OK but not a big winner.