PCM stands for Pulse Code Modulation – the non-compressed format that all computers use for recording and playing sounds. The sound is recorded digitally and the file format is normally WAV or AIF. PCM sound is represented mainly by the sampling frequencies 44.1 or 48 kHz, with a bit depth of 16. This equals a theoretical frequency range of 0–22.050/24 kHz and a dynamic range of 90 dB. Because of an AD/DA conversion low-pass-filter, the frequency range is closer to 0–20 kHz. 

MP3 stands for MPEG-1 Audio Layer 3, an efficient coding algorithm that is based on how our ears work. The algorithm is derived from the fact that we cannot hear concealed frequencies in sounds. Due to a reasonably good sound quality at low bit speeds (normally 128 kbit/s), the MP3 format has been the most popular method for sharing and transferring music and sound. The greatest advantage of MP3 is that it is compatible with all existing music players on the market. 

AAC stands for Advance Audio Coding, a newer and more efficient compression algorithm. It is part of the specifications for MPEG-4 and comprises a large number of different compression algorithms for various media. The audio file can be quite small but the quality is still high. This format is used for distributing music on iTunes. 

WMA stands for Windows Media Audio, a sound format developed by Microsoft. It is effective at high and low compression levels. The newest version can store high resolution and surround sound and can also secure files against copying. WMA is an integrated solution for copy-protected distribution of media with content of a quality level ranging from mobile phones to HD. 

AC-3 stands for Audio Codec 3/Advanced Codec 3/Acoustic Coder 3.
This format is one of the standards that was developed for audio on DVDs. It uses the theory behind MP2 and is roughly the same age. AC-3 also contains metadata functions so that it works in accordance with the set-up of the DVD player, e.g. down-mixing, dynamic range control and dialog normalisation. 

DTS stands for Digital Theatre System. DTS is often regarded as the best sound quality format for DVD videos because it has a higher bit rate than AC-3. It also functions as a surround sound format for audio CDs. 

Audio CDs are the well-known Red Book standard CD that contains up to 80 minutes of indexed sound with a resolution of 44.1 kHz and 16 bits at a bit speed of 1411 kbit/s. It includes functions such as text CD, ISRC and EAN coding. 

Audio CDs with ROM content combine music with multi-media. This type of CD can be played on all CD players, but it also offers an interactive multi-media experience when it is used with a PC or a Mac. The Audio CD + ROM format makes it possible to add videos, pictures, Web links and other file content. Basically, it is an ordinary audio CD with extra benefits.

PCM and stereo AC-3 are obligatory audio formats on DVDs. All players can play these formats, which is why one of them must be used for video DVDs. The introduction of DVDs made it possible to use the MPEG-2 audio format in Europe, but most players today do not support MPEG-2. Surround sound (5.1 channel) is coded as AC-3 and/or DTS. 

Audio DVD is a standard format for high-resolution PCM sound on DVDs. The resolution can be up to 96 kHz with 24-bit surround sound, or 192 kHz with 24-bit stereo. In addition to high-resolution audio, the disc can be used as an ordinary video DVD or ROM. Standard audio DVDs can only be played on compatible players, while audio DVDs with video material can be played on all DVD players.