I've been meaning to reply to this thread for some time, not so much for the debate as to get something off my chest.
We're saddled with CD quality audio because that was the state of the art during the 1980's.
Across recording, mastering, distribution, storage and playback, we had better formats very soon afterwards, but Sony and Philips were impatient.
CD bandwidth extends to 20kHz, and I certainly can't hear above 20kHz any more, but is that all that counts?
I've been struggling to reconcile subjective and objective measures for a long time, but think I'm getting somewhere.
I now think measurements matter more than I ever thought before, but they have to be the right measurements.
It's convenient to focus on the most favourable measures at 1V 1W 1% 1dB 1kΩ 1kHz 1µV etc. but I think we need to look harder.
I think what really counts is how fidelity is maintained around the whole of the audio envelope - a virtual cube that characterises amplitude, frequency and load.
And fidelity has several essential parameters - amplitude linearity, frequency linearity, and phase linearity.
My view is that good audio requires an envelope that encompasses everything we can hear, plus linear responses over the whole of that envelope (not just in the middle).
There's traditionally been more focus on amplitude and frequency linearity, but I think phase linearity is important too.
Anyone who's heard a good infinite baffle subwoofer will know how linear phase response and low group delay makes bass sound better.
In the mid range, speaker cross-overs often mess up phase response where our ears are most receptive, and single drive unit speakers like electrostatics have magical transparency in the mid range (if less so at frequency extremes). However, really effective DSP like Trinnov, Audiolense, Dirac, Neumann, Genelec etc can help to restore that.
At high frequencies, format limitations come into play, because there isn't enough room for the reconstruction filter between 20kHz and the Nyquist frequency, 22.05kHz.
We want amplitude, frequency and phase linearity at all frequencies, but DAC filters can only get two out of three right.
There are lots of options - linear phase, minimum phase, fast roll-off, slow-roll-off, hybrids etc. Each one is a compromise, and at 44.1kHz you never get all 3 linearities right.
The reason for this post is because here at ASR, jkim has posted his detailed measurements of the high performing
JCALLY JM20 MAX: USB-C Headphone Dongle.
Like some of the recent
Soundstage reviews, he measured amplitude AND phase response vs frequency.
With 44.1kHz sampling, the FR is flat to 20kHz, but the phase response deviates by hundreds of degrees within the audio bandwidth.
With 96kHz sampling, the FR is still flat to 20kHz and beyond, but the phase only deviates by tens of degrees within the audio bandwidth.
Soundstage reviews show a wide range of compromised results.
Why does this matter? It doesn't matter for frequency response and tonal accuracy, but it directly impacts transient and time domain behaviour.
While it's true that uniform frequency response is essential for accurate transient response, uniform phase response is essential, too.
So, no, it's not about ultrasonic hearing and golden ears and all that, its about get getting all aspects of fidelity right WITHIN the audio envelope.