What Is PCM Stereo Surround?by David Lipscomb
Pulse code modulation, or PCM, is the digital representation of analog signals. In the case of surround sound, this means that all digital surround formats eventually are decoded as PCM. Pulse code modulation is also found as stereo signals, such as digital PCM from a CD player over a fiber optic or digital coaxial cable.
Commonly-recognized formats such as Dolby Digital and DTS, long used in DVD and other surround formats, are methods of compressing and storing PCM stereo and surround. The sound quality of each format is determined by how much or how little the PCM content is compressed. DTS is compressed less than Dolby Digital, which is why many report the format as sounding superior.
Blu-ray formats such as Dolby TrueHD and DTS Master Audio are very slightly compressed pulse code modulation formats. This means that they are stored in a similar fashion as a computer zip file. Although the PCM-coded content is mildly compressed, when played back it is a bit-perfect facsimile of the master recording. DTS Master Audio is the Blu-ray audio format standard.
PCM stereo and surround audio is sent from source to receiver in a variety of ways. Optical, digital coaxial, and High Definition Multimedia Interface or HDMI are the most common consumer-level methods of getting PCM audio. Of these, only HDMI is capable of transmitting uncompressed PCM, due to far larger bandwidth capabilities.
Essential to PCM sound quality is increased bit depth and bit rate. This is roughly translated as the amount of data per second that is transmitted to the receiving device, such as a surround sound receiver or processor. The higher the bit rate, the better the sound can be. Bit depth is related to the amount of digital samples taken of the analog master. The more samples taken, the more faithful to the original. For example, compact disc audio is normally at 16 bits, while better-sounding formats such as DVD-Audio and Blu-ray formats operate at 24 bits.
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