Hi-Rez Highway

Posted by Isaak J. Garvey (P) on June 28, 2017 at 20:09:45

From Computer Audiphile, a thread started by the author of one of the best sample rate conversion software packages SOX.

The emperor's clothes are slowly but surely being ripped away, thread by thread.

"For months, I have been suspecting MQA to use minimum phase resampling. Years ago I did a test with sox: take a 24/96 file with verified ultrasonic content, and derive a 16/44.1 file from this (using minimum phase resampling) and then upsample it back to the original resolution: 24/96. I cropped both files to one minute, and put up two files on my web server: a.wav and b.wav, put the links on some forum and the shootout started.

We had a lot of hifi professionals listen to these files, as well as studio engineers. Most could not hear the difference. One was cheating by looking at the spectrum with his audio editing tool, and one ultra high-end dealer claimed to correctly identify the real highres file. All others did not hear it and reacted: wow great resampler you have there.

Why minimum phase? Minimum phase corresponds to what MQA is pursuing: it does not add pre-ringing, but moves all the errors to post-ringing, to which our hearing is not sensitive. MQA also tries to get rid of the post-ringing in their rendering phase, which is why MQA sounds so different from the master. If this is better or different is subjective, but I personally do find MQA files decoded on the Brooklyn to have more echo and reverb than the original DXD masters, but voices are ruined. Some of the vocal qualities are gone and it sounds polished.

However, MQA is also trying to solve a problem which is not a problem, that is to get rid of the postringing of minimum phase resampling:
Transient sharpness is guarded as no pre-ringing is added sucking up dynamic range to which our hearing is sensitve, but we don't cut of the tail, which is the main cause for the sound difference with full MQA decoding. Full MQA decoding is no longer master quality but a polished version.

Brian Lucey has already stated that MQA sounds thinner than the original, and with more distortion.

https://www.gearslutz.com/board/12548751-post460.html
https://www.gearslutz.com/board/12551196-post482.html

This is logical: the post-ringing energy in the tail that MQA tries to get rid of, needs to be distributed to some other place in the waveform, causing distortion such as aliasing and HF noise. MQA created a solution for a non-existing problem.

Here we propose and elegant solution using sox minimum phase resampling to upsample undecoded MQA files back to it's original samplerate, with virtually indistinguishable sonic difference from the real studiomaster file that was used to create the MQA version. Any power user with basic command line skills can test these claims.

If developers of music players start implementing minimum phase as a selectable resampling method, it will upsample MQA to what the original master engineer had intended, without the MQA sauce that tries to get rid of the post-ringing, but trades this with new artifacts."

Full post and thread below.

• https://www.computeraudiophile.com/forums/topic/33766-upsamp   (Open in New Window)