# How to upsample voice properly?

I have a low quality 24 kHz mp3 voice and I'd like to upsample it to 48 kHz for farther mixing with another 48 kHz track.

What is the right steepness curve in this case? I'm going to use an ideal low-pass filter with:

Filter steepness=2000
Cutoff shift=1
Pre-ringing=1


but I'm not sure if that would create noise/artifacts or degrade the signal?

Upsample with steep curve:

Reduced steepness:

Low steepness creates artefacts.

• Thank you. Could you explain why an ideal low-pass filter (with maximum steepness) is bad in this case? I'm trying to save as much information as possible. What Pre-ringing is better? Aug 31 '21 at 18:19
• They call it ideal low-pass filter in the docs: s3.amazonaws.com/izotopedownloads/docs/rx8/en/resample/… I updated the post. Aug 31 '21 at 18:51