Today, efficient coding techniques are a must for cost-effective processing of digital audio and video data by computers. Data reduction of moving pictures and sound is a key technology for any application with limited transmission or storage capacity. In the recent years, a lot of progress has been achieved. While there (still) exist several proprietary formats for audio and video coding, the ISO/IEC standardisation body has released an international standard ("MPEG") for powerful audio and video coding tools (see: Overview about the ISO-MPEG Standard - or: What is MPEG all about?).

Without data reduction, digital audio signals typically consist of 16 bit samples recorded at a sampling rate more than twice the actual audio bandwidth (e.g. 44.1 kHz for Compact Disks). So you end up with more than 1400 kbit to represent just one second of stereo music in CD quality. By using MPEG audio coding, you may shrink down the original sound data from a CD by a factor of 12, without losing sound quality. Factors of 24 and even more still maintain a sound quality that is significantly better than what you get by just reducing the sampling rate and the resolution of your samples. Basically, this is realized by "perceptual coding" techniques addressing the perception of sound waves by the human ear (see: Basics of Perceptual Audio Coding - or: What is the trick?).

Using MPEG audio, one may achieve a typical data reduction of

still maintaining the original CD sound quality.

By exploiting stereo effects and by limiting the audio bandwidth, the coding schemes may achieve an acceptable sound quality at even lower bitrates. Layer-3 is the most powerful member of the MPEG audio coding family. For a given sound quality level, it requires the lowest bitrate - or for a given bitrate, it achieves the highest sound quality (see: Advanced Features of Layer-3 - or: Why does Layer-3 perform so well?).

Some typical performance data of Layer-3 are:

*: Fraunhofer uses a non-ISO extension of Layer-3 for enhanced performance ("MPEG 2.5")

All in all, Layer-3 is the key for numerous low-bitrate, high-quality sound applications (see: Applications - or: Layer-3, what is it good for?).

Real-time Layer-3 players

WinPlay3

"WinPlay3" allows the decoding simply by software on any Pentium PC in real time. A 80486 class CPU with a built-in floating-point-unit will also allow some limited operation. For the availability of supported modes, please refer to the following performance matrix:

*downmix: the original stereo signal will be played back as a mono signal
"MPEG-1" = "MPEG-1 Layer-3", i.e. sample rates 32, 44.1 or 48 kHz
"MPEG-2" = "MPEG-2 Layer-3", i.e. sample rates 16, 22.05 or 24 kHz

On a Pentium-90, WinPlay3 consumes less than 30 % of the CPU power to decode Layer-3 stereo @ 44.1 kHz, or around 5 % of the CPU power to decode Layer-3 mono @ 16 kHz.
At least, a 8-bit stereo sound card is required. For full quality audio, a 16-bit card is recommended. The card´s MCI driver should support sampling frequencies from 8 kHz to 48 kHz.
A standard VGA graphics card is required.
As WinPlay3 buffers up to 4 seconds of sound data due to the limitations of the Microsoft Windows multitasking architecture, around 1 MByte free physical memory must be available.
WinPlay3 runs with the following operating systems: Microsoft Windows 3.1/3.11 (in extended 386 mode), Windows 95 und Windows NT (long file names not yet supported).
WinPlay3 supports file play back of *.mp3 files and direct play from an URL via HTTP. WinPlay3 can simply be integrated as an helper application in common browsers, for example Netscape or Mosaic.
WinPlay3 is available at http://www.iis.fhg.de/departs/amm/layer3/winplay3/.