Because just about everyone has a tape player, the audiocassette continues to be the favored format for audiobooks--as it will for some time to come. But just as new downloadable digital formats are shaking up the music industry, it is near certain that audio publishing will see a significant format shift in the near future.

There are a variety of digital audio file formats. Some are proprietary, meaning that they must be played back using specific software, and some are based on open standards. (For detailed descriptions and comparisons, see the link to the MP3 Handbook FAQ in Resources and Professional Organizations). The three most popular for audiobooks are: MP3, an MPEG-based, open-source, highly compressed format that appears to be the favorite for the present; RealAudio, a proprietary compressed format that is popular for streaming audio, played back on the RealPlayer (which also supports MP3); and Windows Media Audio (.wma), Microsoft's proprietary, compressed format. Many online digital audiobook sellers offer two or all three of these formats.

All three of these formats were designed for music. However, the digital reproduction of spoken audio requires much less dynamic range and fidelity than a musical recording does. Put in the right format, a spoken audio file could potentially be much smaller than a music file. This would translate into faster download times and, more important, a higher storage capacity for portable players (see below). So far, Audible.com has taken the lead in producing a downloadable format optimized for speech. Judging by the expected capacity of a forthcoming portable player, the Diamond Rio 500 MP3 player (2 hours of MP3, 28 hours of Audible.com spoken audio), this format is up to 14 times as efficient as MP3. This "shrinkability" factor makes audiobooks even better candidates for digitization than music.

Another crucial consideration in the distribution of any digital content--e.g., ebooks, music, or spoken audio--is copyright protection. (See Resources and Professional Organizations for a link to one body, the SDMI, that is working to promote secure standards.) The law, along with practical and economic barriers, is considered sufficient to protect publishers and authors from audiotape piracy; but those non-legal barriers do not exist in the case of digital files. The consensus is that a technological solution is needed. In the meantime, Audible.com appears to have the only copyright-protected format specifically designed for spoken audio.

Digital audio files are played back either on a personal computer, using software that is generally free and easily downloadable, or on a portable device. And just as few people choose to read books on their computer, few audiobook listeners like to be tied to their PC. The future of digital audiobooks is in portable devices. Presently the favored portable devices use flash memory. (Flash memory, aka Flash RAM, is a "solid state"--no moving parts--type of constantly-powered nonvolatile memory that can be erased and reprogrammed. It is also used in digital phones and digital cameras, e.g.) This category includes dedicated audio players such as the Diamond Rio 500, as well as PDAs (Personal Digital Assistants) made by companies such as Compaq, Casio, Philips, and Hewlett-Packard. An inexpensive adapter allows the Diamond Rio to play through car stereos with cassette players, and high-end car stereos are now being designed with auxiliary input jacks for these kinds of devices.

A large advantage of downloadable audio files is the elimination of manufacturing costs. Retail prices reflect this savings: e.g., a recent novel by Stephen King costs $40 on tape, and $18 in digital format. Also, the production time involved can easily lead to lost sales. For instance, it often happens that an audio book publisher will underestimate the appeal of a printed book and decline to release it on cassette. Months later, when the book sells well and there is demand for an audio version, the 6-8 month lead time required to manufacture and distribute cassettes could be prohibitive. A company such as Audible.com can record and release an audio book in a matter of days.

Though some books are being made available on CD, two limitations of that medium militate against it. A CD can hold only 74 minutes of audio (compared to the standard 90-minute cassette), and most CD players will not "remember" where the recording was last stopped. The possibilities of DVDs are greater, but the very small number of DVD-players out there, as well as the lack of DVD recorders, makes that medium an unlikely one.