AutoSpeed - The Digital Music Revolution

Despite plenty of AutoSpeed readers being IT wizards, there are also many readers who use their PC in ignorant bliss. And it's those people at whom this article on MP3 technology is aimed. MP3 is the music format starting to make dramatic inroads into car sound technology, and is set to have the same impact that CDs had when they displaced cassette tape as the preferred in-car medium.

MP3, Napster, Burning a CD....what does it all mean for car enthusiasts?

Remember when CDs were introduced and there were lots of arguments about how the new (digital) format was inferior in many ways to the old (analog) format of vinyl records? Remember how people said CDs wouldn't replace the current standard as too many people had record players and huge record collections? Well - sure enough - the world adopted the CD as the music medium of choice. This has also been a great benefit to those of us who enjoy music in our cars, as the CD player has far better quality than cassette tape, in addition to surviving much better in the harsh environment of a car!

But now there is another format, one which is likely to have as much impact on the automotive world as CD technology. Called MP3, it has been emerging (or exploding!) for a number of years now, and with the introduction of more affordable MP3 players for the car, we thought it was time to give an overview of what looks to be the future of music storage. (And by the results of our recent poll, a lot of AutoSpeed readers agree with us!)

What is MP3?

MP3 is the usual abbreviation for "ISO-MPEG 1 - Layer 3". It is not a contraction of "MPEG 3" as some people assume. MPEG stands for Motion Pictures Expert Group. MPEG is a group of people that meet under ISO (the International Standards Organization) to generate standards for digital video and audio compression. Work started on MP3 in 1987 and the MP3 standard was originally formalised and published way back in 1991.

MP3 allows the reproduction of sound utilising less space (either storage space, or bandwidth in the case of broadcasts) than traditional digital formats but while still maintaining acceptable quality.

A CD track of 5 minutes will consume approximately 52 megabytes of storage in its native format. But the same track encoded as an MP3 (at 128kb) will consume approximately 5 megabytes or roughly 10% of the original, with little appreciable quality loss. This means that we can store ten times the number of tracks on a single CD if we were to store them in MP3 format. Imagine, a single disc in-dash CD/MP3 player can store the equivalent music of a 10 disc CD-changer!

How does MP3 achieve this without losing too much quality?

MP3 uses a number of techniques to reduce the storage space required for a given audio track.

Firstly it uses a technique called psycho-acoustic modelling (sometimes referred to as perceptual audio coding).

Psycho-acoustic modelling uses limitations in the human hear to reduce the amount of information recorded. A good example of a limitation is masking. If a strong tone is played at - say - 1100Hz your ear will hear it. If we introduce a second tone at 1000Hz, and the second tone is 18dB lower (ie softer), you will not hear the second tone at all! Tones introduced even further away from the strong tone (say at 2000 Hz) will also be masked, but only if they are a lot quieter than the tone at 1100Hz. There are also effects called pre-masking and post-masking. If there is a significant shift in volume (dB) level, then it is believed that the ear/brain needs some processing time to determine this change. Pre masking is usually only a few milliseconds, but post masking can occur up to 100ms after a noise.

If you are at a party in a noisy room full of people and someone near you is speaking quietly then you cannot hear them. However, if the room were empty you would hear them perfectly. An MP3 encoder doesn't record the person who is speaking quietly in a noisy room, because it "knows" that you won't hear them anyway! This helps save space, without losing (much) quality.

Once the MP3 encoder has finished doing its psycho acoustic modelling, it uses Huffman encoding to store the information in even less space. There are whole papers on the maths behind Huffman encoding, but in a very simplified account it can be said that the encoder uses patterns and some sophisticated binary maths to reduce the amount of storage space required. Kind of like writing "100 x I will not misbehave in school" instead of "I will not misbehave in school I will not misbehave in school I will not misbehave in school I will not misbehave in school" ......but not really. Note that there is no loss of information (sound) involved with Huffman encoding. (Huffman encoding is interesting if you like maths and probably boring as hell if you don't!)

Bitrates

The MP3 format allows for different bitrates. The lower the bitrate of the MP3, the lower the quality (but the storage space will be less also). 64kb is roughly equivalent to FM radio and should reduce a CD track to roughly 5% of the original size. 128kb is close to CD quality for most listeners and most music and will be around 10% of the original size. Some music may be more acceptable at 192kb or even 320kb (but the storage size obviously increases).

It is worth noting that the MP3 standard allows for a wide variety of compression techniques - hence not all encoders are created equal.

While encoding varies in quality enormously, almost all commercial MP3 decoders do an excellent job of decoding the MP3 format - you would be hard pushed to detect differences amongst decoders themselves. Obviously quality of the digital to analogue sound reproduction varies as much as it does in conventional CD units.

Now where do I get these MP3s?

There are a number of ways of acquiring MP3 files. We will discuss the most common.

Creating your own MP3 files

If you have a CD-ROM drive in your computer then it is possible to convert a track from a music CD into an MP3 file on your computer. There are many software programs (called rippers) available that enable you to do this.

Most of the current software is fairly well documented/automated so we won't go in to too much detail here on how to extract MP3s. The basic sequence is:

Insert the audio CD into the CD-ROM drive.
Setup a directory to save the files in.
Name the files accurately (later it makes it a lot easier for you and for others) and press the record/extract/convert button!

Almost all programs will allow the extraction of just a single track if so desired.

Some software will also allow the input of sound via your computer soundcard's microphone. This can allow you to "convert" your old LP or audio tape tracks as well.

Downloading MP3 Files

There are numerous ways of downloading mp3 files from the Web. Napster is probably the most well known, and really the one that brought MP3s to prominence in the mainstream media. But there are some complex legal issues involving the sharing and usage of copyrighted material on the Internet, especially the sharing of individual music tracks. Please note that there is plenty of music available in MP3 format that does have the consent of the artists for distribution. A large number of small independent bands release tracks this way, and some of the large groups have also released promo tracks or live recordings in MP3 format as well.

How do MP3 file sharing networks operate?

There are a number of ways that file sharing on the Web occurs, Napster popularised the following methodology.

Searching Servers

Napster utilises a server (well, a group of servers), and people log on to these servers.

Once logged on, you upload a "list" of the shared files on your machine to the server. (This list includes information like title, artist, size, bitrate, length of track, etc.)

The server then maintains a database of all of the shared files of all of the users that are logged on currently to that server.

Once logged on, you can then search the server for files that match certain criteria. So that you can search for a specific track title, and you will be returned a list of all of the files that match that title. Note that this may include covers of the same song by different artists, and may include duplicates from many other users. Once you have found a file that you are searching for, typically you can double click and the download process begins. Napster sets up an individual connection between your machine and the other user's machine and the file is transferred directly. The interesting thing about this technique is that the MP3 file does not actually get to you via the Napster server itself, but rather it is acquired directly from the other user. This helps the speed of the Napster server but also means that no illegal "music" (MP3) is actually on the Napster server itself! (The operation of the Napster system is under legal challenge by music copyright owners and is likely to alter to requiring the payment of a fee.)

There are a number of other companies/servers which now serve a similar purpose to the Napster servers.

Searching Peer to Peer

Another technique for searching files on the Web is popularised by the Gnutella format. This technique involves linking your machine with a number of other (usually random) users. Again, your machine maintains a list of the files that are currently shared on your machine. However there is not one specific server that maintains a list of what everyone is sharing. What happens when you make a search request is that the request is passed on to the other users, who pass it on to the other users, who pass it on to the other users, etc. and eventually a list of matching files trickle back to your machine. You can then choose the file (MP3) that matches the criteria and a connection is established between you and that user, and the file is transferred to your machine.

Time Taken for Downloads

If you are using a 56k modem to connect to the Internet, a standard size MP3 will take approximately 17 minutes to download. If you were to download that MP3 file in the original CD format it would take 2 hours 20 minutes! It is easy to see the advantage of the MP3 format. If you are on a cable/ADSL/satellite connection it is relatively easy to achieve download speeds where the MP3 transfer time is reduced to something like 2 minutes or less. This means that you can download songs in less time than it takes you to listen to them!

In-Car MP3

OK, now we have MP3 files on our computer - but what if we want to use them elsewhere? Another technology has been developing recently and that has been CD-R and CD-RW. Most computers have a CD-ROM drive which enables you to read CDs, but there are relatively cheap CD-RW drives available now which enable you to write CDs. This means you can save computer programs and files on CD, and you can also create your own normal audio CDs (usable in a standard CD player - such as in your car). Note that you can convert MP3 files into wav files (although they are ten times the size!) and then create your very own audio CD which you can then listen to in most normal CD players. (Some older audio CD players don't like playing CD-Rs though!) Of course if you make just an audio CD you lose all the advantages of the MP3 format, but what if you could find a player that reads the MP3 format?

And yes, there are now around a dozen car CD players that can read "MP3 CDs" as well as standard CDs. Currently, they are part of the high-end in-car audio decks (the Kenwood units are the best known), although expect the technology to filter down to lower price players as time goes by. Since on one CD you can fit around 150 MP3 files (depending on length and quality of course), you can have the equivalent of around 10 normal audio CDs on the one piece of plastic!

There are also some other technologies that enable the playing of the MP3 format in cars. We've even seen whole desktop computers installed in cars just to play MP3s! If you have a notebook computer (for that aftermarket ECU?) then these can sometimes be used to play MP3s too. But a better bet are the hard-disc based dedicated MP3 players that have also been developed. Their advantage is that you literally fit all of your music collection into the one player - that can be thousands of tracks! At this stage these machines are tending to come from less mainstream sources with prices staying fairly high - AUS$1000 is typical. They also generally lack a tuner and have line-level outputs (ie they need an amp). Check the URLs below for more on this type of player.

One thing looks certain - MP3 is the way of the audio future.