MQA Encoding
When audio is encoded into MQA, several things happen, the most important of which are:
- ‘Deblurring’ of the source to remove audible artefacts introduced by analogue-digital converters, mixing and mastering.
- Identifying the musical information and encapsulating it for the highest quality sound.
- ‘Origami’ – folding content into a PCM stream for distribution.
- Embedding instructions for the Decoder and Renderer on how to reconstruct with the minimum impact on the clarity of sound and metadata about the content.
- Embedding the Provenance signature.
Origami is always used when the input sample rate is higher than the ‘transmission rate’.
MQA can be sourced from analogue, or PCM, from A/D modulators or from DSD, but the final output is a PCM stream. Currently, all MQA on streaming services has a transmission rate of 1x (either 44.1 kHz or 48 kHz depending on the ‘family’ of the original).
When the input is PCM, the output stream will have the same bit-depth as the input unless either a) Origami is used or b) the input is DSD or floating-point; in these cases, the MQA stream output will always be 24 bit. So an original at 44.1 kHz/24b will create a 24b file and 44.1kHz/16b will create a 16b file. However an original of 96kHz/16b) will generate a 48kHz/24b MQA file because Origami was used. [1]
Playback
So, an MQA stream is PCM that contains all the audio, information about the audio, instructions for the different ranks of playback (depending on decoder and renderer) and a signature. When the stream is played back, the MQA decoder accesses all these parts and can display, e.g. MQA or Studio, Original sample rate, and so on. A fully-featured MQA decoder can display this information purely from the PCM.
Although the MQA stream knows the original sample rate, we don’t bury information about the original bit depth because it is implicit and irrelevant (given that MQA always encapsulates the full dynamic range of musical information with the highest possible precision).