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 Do MP3 encoders sound different? Pt. 4 Read Pt.1   Read Pt.2  Read Pt.3

 Will Ryu


I played the MP3s and test CD tracks through both my home stereo and my Sony MDR-V6 headphones (details listed below). The songs were encoded at a constant bit rate, forced stereo, at 128, 160, 192, and 256 kbs. All listening was done sighted (encoder and bit rate were known). 

I first compared the MP3s to the original CD tracks, and at 128 kbs I had no trouble discriminating the CD from the MP3s. At higher bit rates this became increasingly more difficult, but even at 256 kbs I believe I could hear differences by concentrating on certain parts of the track which were more susceptible to encoding error. However, since I did these tests sighted, I can’t guarantee that I didn’t imagine some of these differences. So please accept these observations with a word of warning. It is very easy to fool yourself into believing you can hear differences. Purported differences can fade away when you do the test double blind. 


In the "Razumosvsky," at 128 kbs, there is a noticeable softening of the attacks of the strings with all of the encoders. With the Blade and LAME encoders, the viola at one point in the track produced a "boxy" tonality that wasn’t apparent on the CD or with the other encoders. The Xing encoder sometimes sounded a bit "whispy" on the softer, quickly-bowed sections and had a bit of metallic tonality in general. FhG was the best of this bunch at 128 kbs, but still not nearly CD quality. 

The sound improved a great deal at higher bit rates, as is to be expected. The boxiness of the Blade and LAME encoders was much less prevalent at 160 kbs and disappeared at 192 kbs. The Xing remained whispy at 160 kbs, but sounded quite good at 192 kbs. I’d be hard pressed to pass a double blind comparison of these encoders at 192 kbs with this test track. I was actually a bit disappointed because I thought the Razumosvsky track would be more revealing.

"Tears in Heaven"

"Tears in Heaven" produced a different set of artifacts. In the very beginning of the track you can hear high frequency mike or pickup noise. On the CD it sounds like normal, uncorrelated noise, but the MP3s produced a swirling and swishing artifact. Also, the foot tapping lost its eerily real presence and the bell lost its clean decay. For lack of a better description, the Blade encoder sounded a bit "crunchy" in the high end, which might have been caused by an excessive brightness in the sound. The Fraunhofer encoder produced a surprisingly harsh sounding attack on the guitar; it remained quick and sharp, but was artificially crisp and accentuated. Nevertheless, the Fraunhofer encoder produced the best sounding vocals and, again, was arguably the best sounding of the bunch at 128 kbs. 

Many of the aforementioned artifacts disappeared at higher bit rates. At 160 kbs the FhG encoder lost the harsh guitar sound. In fact, most of the swishing and swirling high-frequency artifacts lessened at 160kbs with all the encoders. Nevertheless, the "you are there" imaging and presence was absent, and the tonality in the upper register was not quite right.

I could hear even more concrete improvement by stepping up to 192 kbs. The high frequency tonality especially improved. For example, the percussive bell near the start of the song decays cleanly. At 256 kbs I don’t think I could hear differences between encoders, but none of them quite reached CD quality. It was actually the foot tapping that gave the encoded tracks away. Listening to the CD, you can almost see the shoe tapping the wooden stage (I’m not kidding!). Listening to the encoded tracks, you could only hear it.

"Setting Sun"

"Setting Sun," by the Chemical Brothers, was a more revealing test track than I initially thought it would be. In general, the sound was harsh and unpleasant for all the encoders at 128 kbs. There's a lot of high-frequency information in this song, and it might have given the encoders some trouble. Specifically, all of the encoders had difficulty reproducing one percussive track (it sounds like a pitch-shifted snare drum). The Blade encoder was the worst offender, adding a click or a knocking sound to this track. This was a gross enough deviation from the sound that I would call it an encoding error rather than just a general MP3 artifact (this went away at 160 kbs). The harshness remained at 160 kbs, but things were much cleaner at 192 kbs. In addition to the high end harshness, the mid register sounds became unfocused and diffuse at low bit rates. Again, this might have been caused by problems with encoding the high frequency overtones. The distinctive bass drum beat sounded fine at 128 kbs and above.

The envelop please:

Low bit rate winner (128 kbs):

Fraunhofer. It was no contest. While not CD quality, the FhG encoder was sonically the least offensive. And with its superior measurements, it clearly beat out the other encoders at 128 kbs. If you have a tiny hard drive or a portable MP3 player with only 32 MB of memory, this is the encoder to use.

High bit rate winners (192 and 256 kbs):

Fraunhofer, LAME, Blade, and Xing (in order of preference). At the higher bit rates they don’t all sound the same, but the encoders in general were very listenable. I found the Xing high frequency measurements a bit worrisome, but at 256 kbs I thought the Xing encoder sounded as good as the rest. If you are "Napsterizing" some music, I think 192 kbs is a good compromise between sound quality and download times. For my personal MP3 CD-R disks, I encode at 256 kbs. This is still more than 7 CDs on one CD-R.

Parting shots

The most popular bit rate for MP3s is still 128 kbs, by a wide margin. Certainly MP3 trading on the internet is still dominated by 128 kbs, and many MP3 web sites still encode only at 128 kbs. This is understandable. 128 kbs MP3s played over an average computer sound system is very listenable, and listening to 128 kbs files on a portable player in an environment with moderate ambient noise sounds just fine. 

The problem with 128 kbs occurs when you take the MP3s from a typical computer desktop environment and move them into a serious listening environment. With the increased importance of sound reproduction for computer gaming and DVD video viewing, the average computer speaker system is of higher quality than it was the past. In addition, stand-alone MP3 players like the Apex AD-600 untether the MP3 music format from the computer and bring it to the higher fidelity home stereo. Thus the listening conditions for MP3s have changed, but the standard bit rate of MP3 encoding hasn’t. If you can’t hear the difference between 128 kbs and 192 kbs then congratulations, the more hard disk space to you. But if you can, why settle for 128 kbs? Hard drives are getting larger and computers are getting faster. Mpeg-1 Layer III audio is uniquely suited to match the velocity of these technological changes. So please, for the sake of high fidelity, let’s step up the bit rate.

Technical Info:

Computer equipment: Celeron 450, Kenwood True-X 42x SCSI CD drive, Adaptec 2930CU, Western Digital Expert 18.1G drive, Smart and Friendly 4x SCSI CD-R.

Ripping & encoding: CD tracks were ripped with Exact Audio Copy v. 0.9 preBeta 3. Wav files were trimmed in Cool Edit 96. Encoders used were described above. MP3 to wav conversion was done by Cdex 1.2. CD-Rs were burned with Easy CD Creator 4. Programming for power spectra and MSE measurements were done in Labview 5.1.

Audio Equipment: Apex AD-600a, Audio Alchemy DTI (dejitter device), Audio Alchemy DDE 3.0 (D to A), AudioPrism Debut 40W tube amplifier, Reference 3a Royal Master Monitors, Sony MDR-V6 headphones.

 Copyright 2000

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