MQA-CD

MQA-CD refers to an audio disc that embeds MQA (Master Quality Authenticated) encoded signals within a standard CD-DA structure. The disc still complies with the audio CD specification in terms of physical structure, track organization, and basic PCM parameters, and can therefore be read by a standard CD player; “MQA-CD” describes the encoding method used in CD-DA audio; it is not a new type of disc with higher capacity or requiring a different laser system.

CD-DA can only store 44.1 kHz, 16-bit stereo PCM. When creating MQA-CD, the source signal is MQA-encoded, with some information and control data placed in the lower significant bit region of the 16-bit PCM, accompanied by noise shaping. In the absence of an MQA decoder, the player outputs it as standard 44.1 kHz PCM; once a compatible decoder recognizes the embedded flag, it can perform the expansion and reconstruction processing defined by MQA. What MQA refers to as “folding” is not a bit-for-bit lossless compression of high-sampling-rate PCM into CD capacity. The encoding preserves the fundamental frequency band and lossily organizes the high-frequency residual information so that it can be hidden in the noise-like region of the lower bits; The signal obtained after decoding is not an exact bit-for-bit copy of the original high-resolution PCM. Whether a decoder performs only the core software unfolding or continues with subsequent rendering depends on device certification and the signal chain.

There are several possible outcomes for the playback path. A standard CD player may output the base PCM directly; players with MQA decoding capability can recognize the signal from the disc or digital output; certain devices are responsible only for reading the disc and must pass the unadjusted digital data to an external decoder. If digital volume adjustment, equalization, sample rate conversion, or other processing that alters the low-order data occurs before the signal reaches the decoder, the MQA flag and embedded information may not be preserved. Once analog output has completed the digital-to-analog conversion, downstream devices cannot restore the MQA expansion in the digital domain.

The difference in sound quality between MQA-CD and a standard CD cannot be inferred solely from the disc label. The final product is also influenced by the master used, the MQA encoding parameters, the CD layer signal, and the playback path; Even for the same album, the MQA-CD, standard CD, and download versions may use different master recordings. Some releases use UHQCD or similar disc materials to manufacture MQA-CD; this is a combination of media manufacturing processes and signal encoding, and the two are not the same technology.