TidBITS: Making MP3s

Article 1 of 2 in series

01 Nov 1999 | Print

Making MP3s, Part 1

Although MP3 is turning into a great way to expose yourself to new music - like the new single "Icicle" from local Michigan band Troll for Trout, or Alan Parsons' "DrShow full article

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Although MP3 is turning into a great way to expose yourself to new music - like the new single "Icicle" from local Michigan band Troll for Trout, or Alan Parsons' "Dr. Evil Trance Remix" of the title track from his new album - half the fun is in rolling your own. Happily, there are no fewer than five separate Macintosh applications available for creating your own MP3s. With one exception, all of them let you encode MP3 files directly from an audio CD - and they'll do it faster than real-time with a reasonably speedy CD-ROM drive and processor.

<http://www.mp3.com/artists/16/michigan_rocks_ 99.html>
<http://www.amazon.com/exec/obidos/subst/music/ download/alan-parsons/ap-main.html>

Making MP3 files of CDs you already own and playing them back on your own equipment is perfectly legal. Making MP3 files of music you've created and giving them away is also legal. But uploading and downloading "bootleg" MP3s (songs encoded from commercial albums without the artist's or record label's permission) is illegal. Remember, it's up to you to keep your use of MP3 players and encoders on the light side of the Force.

We donned headphones and put together a four-minute AIFF audio file containing several different styles of music, and next week we'll tell you how quickly our five contenders encoded MP3 files and how these files sounded. But first, a journey into the psychology of sound.

Why Encoders Matter -- When you make a 128 kilobit per second (Kbps) MP3 file from an audio CD, the encoded file is less than 10 percent of the size of the original, which means that the encoder essentially discards over 90 percent of the original data. It's been known for decades that our sense of hearing is as much between our ears as it is in them. By taking advantage of our knowledge of how humans perceive sound (the science of psychoacoustics), it is possible to extract the most important parts of an audio signal and encode them with high fidelity, using lower fidelity for less noticeable parts of the sound, or discarding such parts altogether. This is the basic principle behind MP3 and other lossy audio compression schemes, such as the QDesign Music Codec built into QuickTime.

One interesting fact about the MPEG standard (of which MP3 is only one small part) is that the specification says nothing at all about how an MPEG encoder should work - it only defines the format required by the decoder. This means that developers are free to innovate their own encoding schemes - as long as the resulting file has the right format, it can be decoded by any MP3 player. Competition, the theory goes, will drive developers of MP3 encoder software to develop better and better psychoacoustic simulations. Better encoders mean better-sounding MP3 files - and the best part is that you don't need new playback software to enjoy the improvement, just a new version of the file.

So, counterintuitively, the software used to create an MP3 file can have as much or more effect on its sound quality than the software you use to listen to it. Although some MP3 playback programs have built-in equalizers and other enhancements to allow you to shape the sound to your liking, all software MP3 players sound pretty much the same with those features turned off.

The good news is that the encoders we tested produced listenable MP3s at bitrates of 128 Kbps and higher regardless of the style of music. Bitrate is just a fancy word for how many bits are required to encode a second of music. The more bits you use, the less audio information you have to throw away, and thus the better the resulting file sounds, all other things being equal. If the bitrate of an MP3 or QuickTime file is lower than the bitrate of your modem (generally 56 Kbps or lower), and the planets are aligned just right, you can actually play back the file as it downloads. Most stereo MP3s you'll find on the Internet are encoded at 128 Kbps or higher, which means you'll need ISDN or better to listen to them in real-time.

In naked ear tests, you'd be hard pressed to notice any differences between the files encoded by our selection of audio bit-crunchers. With headphones, some minor differences become apparent, although nothing earth-shattering was revealed until we conducted a torture test, encoding stereo files at bitrates of 64 Kbps and lower. At this point, a number of encoding inaccuracies (commonly referred to as "artifacts") became apparent as the encoders struggled to decide which parts of the sound were least important and thus disposable. It was obvious which had the best psychoacoustic models under the hood. Tune in next week to see how the different encoders fared in our tests, including AudioCatalyst, SoundJam MP, N2MP3, MVP, and the free MP3 Encoder.

[Jerry Kindall is the founder of Manual Labor, a technical writing and Web design firm specializing in the Macintosh. His music collection includes, at last count, over 900 CDs.]

<http://www.manual.com/>

Article 2 of 2 in series

08 Nov 1999 | Print

Making MP3s, Part 2

by Jerry Kindall

The recent popularity of MP3 goes beyond downloading music files from the Internet. Using MP3 encoding software, you can make MP3 files from music CDs you already ownShow full article

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The recent popularity of MP3 goes beyond downloading music files from the Internet. Using MP3 encoding software, you can make MP3 files from music CDs you already own. The first part of this article discussed the ins and outs of MP3 encoding (see "Making MP3s, Part 1" in TidBITS-504); this week we present the results of donning headphones and making MP3s from five popular encoding programs.

<http://db.tidbits.com/article/05636>

Xing AudioCatalyst 2.0.1 -- AudioCatalyst was the first fast MP3 encoder for the Mac, and the first that could encode audio directly from CD without first saving it to your hard disk. While the initial release didn't have all the features of its Windows predecessor, AudioCatalyst 2.0 now enjoys parity with its Windows sibling.

<http://www.xingtech.com/mp3/audiocatalyst/>

The program feels like a Windows port, and its options are buried in different dialog boxes. Still, it sports a number of features its competitors don't. For one thing, it can automatically normalize the volume level of CD tracks before encoding them. (Many older CDs are mastered at comparatively low levels. Normalizing boosts the signal to take advantage of the full available dynamic range.) It also has a function to snip silence from the beginning and the end of a track automatically.

AudioCatalyst's panoply of features defined our expectations for other MP3 encoders. AudioCatalyst can look up track names for audio CDs from the Internet CD Database (CDDB), so you don't have to name the resulting files, and it enables you to specify how you want the files to be named (e.g., track number + song title + artist name) and will optionally create a folder for each album and yet another enclosing folder outside that named after the artist.

<http://www.cddb.com/>

AudioCatalyst was the first Mac MP3 encoder to create MP3s with the full audible frequency range from 20 Hz to 20 KHz. (Older MP3 encoders cut off frequencies at 16 KHz.) At sufficiently high bitrates, this brings MP3 closer to CD-quality realism, although at lower bitrates, this barely audible data can cause the representation of the rest of the audio spectrum to suffer. Like almost all its features, AudioCatalyst lets you turn off extended-range encoding.

AudioCatalyst pioneered variable bitrate encoding (VBR), a feature that automatically increases the number of bits used to encode complicated or dense passages of music, while using a lower bitrate for simpler passages. Standard MP3 encoding, sometimes referred to as constant bitrate or CBR, uses the same number of bits per second throughout the file. VBR can substantially increase the quality of some MP3s with only a modest increase in file size. Some older MP3 players can't play VBR files, and neither can QuickTime 4, but most current players can handle them.

AudioCatalyst is the only program in this roundup that can MP3-encode live audio from your computer's microphone or audio line inputs. With the other encoders, you must first record the audio to an AIFF-format audio file using a program like the free Coaster, then encode that file as MP3.

<http://www.in.tum.de/~rothc/coaster.html>

If you need one of the features only AudioCatalyst provides, or if you will be converting a whole flock of files, no other program even comes close to offering as much functionality as AudioCatalyst. At $30, it's price-competitive with the other full-featured encoders in this roundup, and it's by far the most flexible. It's also one of the fastest and produces very good-sounding files. (In our low-bitrate torture test, it came in second.) However, the program's user interface is unnecessarily cluttered and complicated, so if you just want to convert a few favorite songs to MP3 without much fuss, one of the other programs would probably be better.

Casady & Greene SoundJam MP 1.1 -- SoundJam MP is both an MP3 player and an encoder. It can act as an audio CD controller and play streaming MP3 broadcasts from the Internet as well. (See "That MP3eaceful, Easy Feeling, Part 2" in TidBITS-501 for more on SoundJam.)

<http://www.soundjam.com/>
<http://db.tidbits.com/article/05603>

SoundJam is a good choice if you want to create MP3s and listen to them in a single program. Like its playback-only competitors Audion and Macast, it comes with a variety of "skins" for changing the program's appearance and supports both audio and visual effects plug-ins. It's the only player that supports Arboretum's Realizer plug-in, which is a fancy alternative to an equalizer that employs psychoacoustic principles to boost the audibility of bass on small computer speakers, enhance the stereo image, and synthesize missing high frequencies.

Despite getting high marks for value, SoundJam's current encoder functionality isn't competitive with the other encoders. The program has CDDB support for automatically naming your files and can create an enclosing folder named after the album. It also supports optional full-frequency (20 Hz to 20 KHz) encoding and can automatically switch out of this mode when encoding at lower bitrates. Even when encoding the full frequency range, however, SoundJam-encoded files sound a little soft and muffled compared to MP3s made by other programs. (Judgments of sound quality are extremely subjective, and there is little difference between any of the programs we looked at for bitrates of at least 128 Kbps. SoundJam 1.1 didn't do well on our torture test, unfortunately.)

The authors of SoundJam are aware of the product's sonic shortcomings and are working diligently to remedy them. After we published the first part of this roundup, Jeffrey Robbin sent us a beta version of a new version of SoundJam. He noted that some of the features weren't finalized, and in fact they weren't even sure what version number it would be, but he thought we'd find the sound quality much improved. And indeed it is. This beta version of SoundJam MP fared much better on our low-bitrate torture test, with very few artifacts, although it accomplished this feat by severely restricting frequency response - the resulting MP3 sounded more like AM radio than a CD. Still, we'll take a musically coherent but muffled MP3 over an artifact-infested one that's almost unintelligible, and the new SoundJam gave us fewer artifacts on the low bitrate file than all but one of the other encoders. At more typical bitrates, the muffled character we noted in version 1.1 was much reduced. The program has also added variable bitrate support and a feature that lets you strip out bandwidth-robbing inaudible frequencies below 10 Hz.

SoundJam already has the distinction of being the only MP3 encoder that takes advantage of Apple's new Velocity Engine. On a Power Macintosh G4, assuming you can get one, it's the fastest MP3 encoder you can buy, at least until Proteron delivers a promised upgrade to N2MP3. If you want a good deal on a multimedia player and encoder, SoundJam is worth checking out as it stands. The upgrade we tested will likely render it a strong competitor on the merits of its encoder as well.

Proteron N2MP3 -- Although we're at a loss to explain its name, Proteron's new MP3 encoder benefits from the most intuitive user interface of the programs in this roundup. It's so beautiful that it makes you wonder why every MP3 encoder doesn't work the same way. If this program doesn't win an Apple Human Interface Design Excellence (HIDE) award, something is seriously wrong.

<http://www.n2mp3.com/>

Here's how it works. You put an audio CD into your computer's CD-ROM drive. As it mounts, the name of the desktop CD icon changes to the title of the CD you just put in, thanks to a quick CDDB look-up. You open the CD icon, and inside you find icons for the individual songs. N2MP3 tweaks this window, too, so you can see the title and duration of each track. To convert a song to MP3, double-click it to save it on your desktop (or another previously designated folder), or drag the song icon from the CD to any folder. The N2MP3 progress window pops up and a few minutes later, your fresh MP3 file is out of the oven. N2MP3 also provides a convenient way to encode audio tracks on Enhanced CDs (which don't show up on the Finder desktop as audio CDs) and uncompressed AIFF audio files.

The encoder barely has a user interface at all - just a few dialogs that let you choose encoding settings. Although the settings aren't as multitudinous as those in AudioCatalyst, they are far better organized, and aside from one minor omission, all the essentials are there. Although N2MP3 supports full-frequency range recording, you can't turn off the feature as you can in AudioCatalyst and SoundJam, which hinders its encoding performance at low bitrates.

You can choose encoding settings in a dialog that pops up at the beginning of each encode operation, or you can choose them in the N2MP3 Settings control panel and bypass the pre-encode dialog entirely. This "fast track" method is the closest thing to having MP3 encoding built into the Mac OS.

There's a unique play-during-encode feature, which of necessity limits the program to encoding at real-time speed. For fastest encoding, turn it off. We were slightly disappointed, however, to discover that this feature played back the original audio rather than decoding the compressed audio, so you can't hear what your encoded file will sound like. (We were hoping it would be like the tape monitor switch on a three-head tape deck.)

Like AudioCatalyst, N2MP3 offers variable-bitrate encoding, but provides more control. In AudioCatalyst, you can choose only one of five quality settings subjectively labeled from Low to High. With N2MP3, you set the minimum bitrate using the same slider you use to set the bitrate of a fixed-bitrate file, and then use a second slider to tell the program how good you want the file to sound; higher quality naturally implies additional bits. The manual reveals that when the slider is set to Better, the encoding bitrate for each split-second frame of the encoded MP3 file is automatically increased until there is virtually no distortion for that frame. As you move the slider closer to the Worse end of the scale, N2MP3 places lower and lower limits on the number of bits that can be added to each frame.

This is a powerful feature hidden in an obscure location and woefully under-explained, so we'll rectify that omission here. To make the best-sounding MP3 file the program is capable of without wasting unnecessary bits, choose the lowest possible base bitrate (32 Kbps) and drag the VBR quality slider to Better. Each frame of the file will then use the number of bits required for best results, and no more. It's a bit counterintuitive that a Better VBR file with the slider set to 32 Kbps can be significantly larger than one encoded with a constant base bitrate of 128 Kbps, but no other encoder offers such an easy way to get the best sound quality with the smallest file.

When set to its Fast mode, N2MP3 is the fastest encoder in this roundup, beating AudioCatalyst by a few seconds when compressing a 4-minute file on our 300 MHz G3 machine at constant bitrates. Although files encoded in this mode exhibit a slight sibilance (exaggerated high-frequencies during "sss" sounds) compared to the original, they are acceptable. (Proteron says that their encoder is optimized for 160 Kbps encoding, and the sibilance all but vanished when we tried again at that rate.) N2MP3 is significantly slower in Best Quality mode - in fact, it was slower than all but one of the other encoders, and that other encoder is free. In our torture test, N2MP3 was soundly trounced by AudioCatalyst. At ordinary bitrates (128 Kbps and above), though, N2MP3 held its own.

QDesign MVP 1.0 -- QDesign is no stranger to digital audio compression; their music compression technology was deemed worthy of incorporation into QuickTime 3 and 4. MVP is, like Casady & Greene's SoundJam MP, intended to be a combination multimedia player and encoder. (That's not the only thing they have in common, since the MP3 encoder in SoundJam is licensed from QDesign.) MVP even plays back QuickTime video and has features for finding, downloading, and buying music.

<http://www.mvpsite.com/>

MVP's encoding options are even more limited than SoundJam's. You get to choose the (fixed) bitrate for encoding. And that's it. MVP does have CDDB lookup for automatic naming of files and gives you AudioCatalyst-style flexibility in name formats, but the program inexplicably cannot encode AIFF files to MP3, which excluded it from our time trials. With luck, QDesign will add this invaluable feature in the future. Files it encoded also suffered from the same slightly "soft" sound as SoundJam, for obvious reasons.

One point in MVP's favor is that it looks really nice (nicer than most of the "skins" available for SoundJam, Macast, or Audion, even though you can't change MVP's appearance) with an enormous track title display. It's also extremely simple to use and costs only $20.

Macromedia SWA Export Xtra & Lindvall MP3 Encoder 0.12 -- Macromedia Director's Shockwave Audio (SWA) feature enables Director files (embedded in Web pages through the company's Shockwave plug-in) to include streaming audio. Although Macromedia doesn't promote the fact, SWA is essentially MP3. The SWA Export Xtra is a plug-in for the company's SoundEdit 16 audio editor, which costs about $300. But fear not, ye cheapskates - Johan Lindvall has written a little application called MP3 Encoder that supports just enough SoundEdit 16 plug-in voodoo to run the SWA Export Xtra and to remove the SWA-specific bits of the file before saving it. It's free, and so is the plug-in. Voila, instant free MP3 encoder.

<http://www.macromedia.com/support/soundedit/how /shock/sound_devtools.html>
<http://www.dtek.chalmers.se/~d2linjo/mp3/ mp3enc.html>

No one will mistake MP3 Encoder for AudioCatalyst. Its user interface is almost as minimal as MVP's. You can't encode directly from audio CDs; instead, you must use MoviePlayer or the freeware Track Thief to create AIFF audio files, which require about 10 MB per minute of music.

<http://www.student.nada.kth.se/~d88-bli/misc/>

The SWA Xtra lacks variable bitrate support; nor can it encode the full audible frequency range (it only goes up to 16 KHz). And it's slow: the two slowest times in our trials were achieved with this software in Normal and Higher Quality mode. But it does work - very well, in fact, despite its limited frequency response. This encoder did better on our low bitrate torture test than any of the other programs. And did we mention it's free?

The Final Note -- All of the MP3 encoders in our roundup have at least one reason to recommend them, and all produce reasonable files at typical bitrates. MVP plays a wide variety of multimedia files and is the least expensive of the commercial products. SoundJam is slightly more flexible than MVP, can play Internet MP3 streams, and has the visual bells and whistles of its playback-only competitors. It also comes with Realizer, which can improve sound on typical computer speakers and is attractively priced compared to a separate player and encoder.

N2MP3 produces better-sounding files, is even more configurable, and has a elegant and simple user interface. AudioCatalyst is extremely configurable, very fast, and produces great-sounding files. And the SWA Xtra/MP3 Encoder combination is free and does very nice low-bitrate encoding.

Although we had hoped a single program would pull ahead from the pack, it wasn't meant to be. If we're forced to pick, our vote goes to N2MP3 for most users and AudioCatalyst for audio geeks. In fact, our dream encoder is a cross between the two: Xing's encoder and N2MP3's user interface, with an extra checkbox or two in the Advanced settings to satisfy our tweaker's urge. Nevertheless, the state of MP3 encoding on the Mac has gone from lame to robust in a remarkably short time, and that's a credit to all the developers involved. Try all their wares to see which suits your needs best. You'll enjoy playing with this technology.

[Jerry Kindall is the founder of Manual Labor, a technical writing and Web design firm specializing in the Macintosh. His music collection includes, at last count, over 900 CDs.]

<http://www.manual.com/>

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Series: Making MP3s

Making MP3s, Part 1

Making MP3s, Part 2