Hi all
My upsampling question is centred on what happens with original samples, when using integer vs non-integer ratios (all else being equal with algorithm).
I watched this video by Ayre Acoustics and they mention with non-integer ratios you lose the original samples.
Can someone explain or show this, in the simplest way? If possible
I assumed that no matter what ratio is used, original samples are not affected (all else being equal other than ratios).
I fully understand in practise it probably doesn't matter - no audible difference.
More just wanting to understand better.
This is a great question. I used to worry about this until a member here (apologies - I have a mental block and always forget who it was!) showed me that this is not an issue.
Here's a simple way to understand it, based on the way it was shown to me:
1. My original concern was that if I took a 96kHz file and downsampled it to 44.1kHz - non-integer - I could never get the two files to completely null out when I did a null test with them (line up the waveforms, invert one, then mix them together).
2. The member here explained to me that because of the different sample rates you can never do a null test with them that way. Instead, they told me to take that non-integer, downsampled 44.1k version and then resample it back up to 96k, and
then run the null test, comparing it with the original. Because the processed version had been downsampled to 44.1kHz, data had been changed/lost forever, and so upsampling it back to 96kHz would not invalidate the test.
The result when I did this was that the original and the downsampled-then-upsampled version nulled out 100%, total silence,
up to the 22.05kHz Nyquist limit of the 44.1kHz sample rate.
In other words, the 96kHz original's samples are indeed different - when you non-integer resample to 44.1kHz you do lose data.
But the key issue is that the only changed/lost data that cannot be 100% accurately reconstructed is the frequency information that was
above/beyond the Nyquist limit of the lower sample-rate format. And since the Nyquist limit of a 44.1kHz sample rate is still comfortably above the audible range of human hearing, as a practical matter non-integer resampling has zero audible impact.
It blew my mind - and as a side benefit it's really convenient because on-the-fly resampling for music streaming systems therefore becomes convenient but not essential for maintaining true high fidelity sound reproduction.