Editing CD player (section)

===Digital signal processing===
The first stage in the processing chain for the analog RF signal (from the photoreceptor device) is digitizing it. Using various circuits like a simple comparator or a data slicer, the analog signal becomes a chain of two binary digital values, 1 and 0. This signal carries all the information in a CD and is modulated using a system called [[Eight-to-Fourteen Modulation|EFM]] (Eight-to-fourteen modulation). The second stage is demodulating the EFM signal into a data frame that contains the audio samples, error correction parity bits, according with the [[Cross-interleaved Reed-Solomon coding|CIRC]] error correction code, and control data for the player display and micro-computer.
The EFM demodulator also decodes part of the CD signal and routes it to the proper circuits, separating audio, parity and control (subcode) data.

After demodulating, a CIRC error corrector takes each audio data frame, stores it in a [[Shadow Random Access Memory|SRAM]] memory and verifies that it has been read correctly, if it is not, it takes the parity and correction bits and fixes the data, then it moves it out to a [[Digital-to-analog converter|DAC]] to be converted to an analog audio signal. If the data missing is enough to make recovery impossible, the correction is made by interpolating the data from subsequent frames so the missing part is not noticed. Each player has a different interpolation ability. If too many data frames are missing or unrecoverable, the audio signal may be impossible to fix by interpolation, so an audio mute flag is raised to mute the DAC to avoid invalid data to be played back.

The Redbook standard dictates that, if there is invalid, erroneous or missing audio data, it cannot be output to the speakers as digital noise, it has to be muted.