Hi! What is the better filter steepness for resampling from 24 kHz to 48 kHz? Lower steepness makes the range of frequencies at the upper boundary quieter. At the same time, iZotope manual does not recommend higher values: "Higher filter steepness means better frequency performance of the filter: wider passband retains more useful signal, while stronger stopband attenuation provides better rejection of aliasing. At the same time, higher steepness of the frequency response requires a longer filter, which produces more ringing in time domain and energy smearing near the cutoff frequency."

I meant the first one: a signal recorded with a 24k sampling rate [which wouldn't have any audio above 12k anyway] being upsampled to a 48k sampling rate. I hope to add some frequencies above 12k with Spectral Recovery after the upsampling. The problem is that the audio is not initially of very good quality, so it's hard to say how the less aggressive curve affects it. But I clearly see the attenuation of the very highest frequencies on the mel spectrogram. Do you know what these artifacts [ringing, transients] might look like on the mel spectrogram?

1. What if I make the lowest possible curve (filter steepness 5), move it as far to the right as possible (cutoff shift 1.40) and then remove all the frequencies above 12k? Like in this picture: https://i.stack.imgur.com/Gd2U7.png 2. I never thought that upsampling could degrade sound quality. The iZotope RX prompts you to select a curve, but programs such as Audition do not allow you to adjust the curve. How do they work? Audition does not reduce the volume of the high frequencies and does not reflect the frequencies upwards.

I hear a noticeable decrease in volume in the upper frequencies at the default settings. I also see frequencies mirrored up, which I would like to avoid. https://i.stack.imgur.com/NaCyD.png

Thank you. Now I think I'm beginning to understand how it works. Another question about Pre-ringing. Is it better to put 0 or 1 in this case? There are 2 options: "no pre-ringing, but maximal post-ringing" and "the amount of pre-ringing is equal to the amount of post-ringing". How do I find out which is better?