Qobuz FLAC decompress

[tmtomh]

23 minutes ago, KingRex said:

How do they differ.  How does MQA get from 16 something to 24 something without decompressing.  There has to be a operation going on that uses computing resources.  

 

FLAC is lossless compression: It shrinks the file size from the original PCM file (i.e. WAV or AIFF), but no audio data is thrown out or permanently changed. When you play a FLAC file, it's not unfolded; it's decoded.

 

MQA is lossy compression plus in many cases lossy downsampling: Any PCM original with a sample rate of 176.4kHz or 192kHz, MQA resamples to half that sample rate (to 88.2k or 96k), throwing out the higher sample-rate data. Then it further compresses that downsampled data into a file that looks like it has half of that sample rate - i.e. 44.1k or 48k. The data above 44.1 or 48k and below 88.2 or 96k is lossy compressed - meaning some of the data is thrown out and the rest is re-encoded - and packed into some of the lower bits of the 16 or 24-bit bit depth of the file.

Then, depending on your playback system, the MQA file is "unfolded" to various degrees in playback. If you have the full unfold and render, then a 24/48 MQA file in the above scenario would be "unfolded" to 24/96, and then the whole thing would be resampled up to 24/192 - although again, the original data is lost forever, so that 96 to 192k resampling simply doubles all the samples in the 96k file. And again, the samples in the 96k file are themselves only a partial representation of the original, because the "folding" process that stuffed a 96k file into a 48k file container necessarily threw out some of the original data.

 

By contrast, a FLAC file throws out none of the data - it simply packs 100% of the audio data into a smaller file than the original, using algorithms to more efficiently store the data.

 

MQA compression is akin to mp3. FLAC compression, by contrast, is akin to ZIP - a ZIP file retains 100% of the original data. An mp3 does not.

[tmtomh]

21 minutes ago, Cebolla said:

Ok I was being a bit mischievous - not being entirely happy with MQA being described as compressed, given its hybrid nature and dual personality. Partially compressed describes it aptly.

 

I don't care that much about the semantics, so if folks want to call it partially compressed that's fine. But my understanding is that a file is either compressed or it is not. If the data is rearranged and put into a different file format in order to reduce its size, then to my mind that's compression.

 

With MQA in particular, frequencies in the audible range are not compressed in terms of sample rate - an MQA file is 44.1 or 48kHz. But the bit-depth is impacted by the compression, with one or two of the first 16 bits used to store compressed/encoded higher sample-rate data for the unfold. To my mind, that makes MQA a compressed format. 

 

But again, I do not want to get into a semantics fight about whether it's partially compressed or just compressed. The point, IMHO, is that it's lossy, and it's proprietary.

[tmtomh]

4 hours ago, Cebolla said:

MQA, be it in its undecoded state or in its decoded state, is always a PCM audio signal - therefore given that PCM is not compressed, it follows that MQA is not compressed.🙂

Not arguing that MQA isn't lossy, though!

 

I do feel it's important to note that this is incorrect. mp3, AAC, FLAC, WAV, AIFF, and ALAC are PCM too, but they are compressed. Whether or not something is PCM has nothing to do with whether or not it's compressed. If you are using "PCM" to mean, "a PCM source in a file wrapper," that's fine - but then in that case you still cannot say that MQA is not compressed, because it is not just a file wrapper for PCM in the way that WAV and AIFF are, and it is not a lossy, non-destructive wrapper/encoding like FLAC and ALAC are.

[tmtomh]

45 minutes ago, Cebolla said:

That was indeed what I was referring to - the point being MQA is the PCM audio signal source (albeit with something done to it) and therefore not a file wrapper full stop. So, MQA can be losslessly carried uncompressed by WAV & AIFF,  losslessly carried compressed by FLAC & ALAC and even carried lossily (God forbid) compressed by MP3 and the like.

 

Well, sure - but the issue is that this MQA thing that's being losslessly carried by those wrappers is already lossy in and of itself, and is already compressed. 

[tmtomh]

9 hours ago, Cebolla said:

Partially compressed, remember 🙂

I partially remember. 🙂