AI audio upscalers list
More clarity/better quality/general audio restoration of separated stem(s)
Have complete freedom over the result, using (among others) spectral restoration plugins to demudd the results of separations freely with plugins. Then you can use the result further with e.g. AI upscaler or in reverse.
E.g. from plugins, you can start by using Thimeo Stereo Tool which has a fantastic re/mastering chain feasible for spectral restoration useful for instrumentals sounding too filtered from vocals and lacking clarity. Also use Unchirp which states great complement to Thimeo Stereo Tool, although focuses more on the already existing spectrum.
You can also play with free Airwindows Energy/Energy2 and Air/Air2 (or Air3, MIA Thin) plugins for restoration, and furthermore some compressors or other plugins and effects mentioned in the link above.
If you're not afraid of learning a new DAW, Sound Forge Cleaning Lab 4 has great and easy built-in restoration plugins too (Brilliance, Sound Clone>Brighten Internet Sources) with complete mastering chain to push even further what you already got with Unchirp and Stereo Tool.
Izotope RX Editor and its Spectral Recovery may turn out to be just not enough, but the rest of RX plugins also available as VST can become handy, although Cleaning Lab has lots of substitutes for filtering various kinds of noise. Working comfortably in real-time with all the plugins opened simultaneously while combined is more comfortable than RX Editor workflow. But you can use some plugins from RX Editor as separate VSTs in other DAWs including Lab 4. Ozone Advanced might turn out useful too.
Actually, once you finish using the plugins above, now you can try out some of the mastering services and not in the opposite way (although you might want to meet some basic requirements of AI mastering services to get the best results first, e.g. in terms of volume).
Q: AI vocal remover did not "normalize" (I don't think it's the right word) the track on the moment where the vocal was removed, so it's noticeable, especially on instrument-heavy moments.
I make things better by creating a backup echo track by combining stereo tracks with inverted ones and adding this to the main track with -5db, but it's still not good enough. Are there any technics that separate track with not noticeable effects or maybe there is some good restoration algorithm that I can use
A: If vocals are cancelled by AI, such a moment stands out from the instrumental parts of the song.
Sometimes you can rearrange your track in a way that it will use instrumental parts of the song when there are no vocals, instead of leaving AI separated fragments. Sometimes it's not possible, because it will lack some fragments (then you can use only filtered moments at times), and even then, you will need to take care about coherence of the final result in the matter of sound as you said.
At times, even fade outs at the ends of tracks can have decent amounts of instrumentals which you can normalize and then use in rearrangement of the track. E.g. you normalize every snare or kick and everything later in fade out, and then till the end, so it will sound completely clean.
Generally it's all time-consuming, not always possible, and then you really have to be creative using normal mastering chain to fit filtered fragments to regular unfiltered fragments of the track.
You can also try out layering, e.g. specific snare found in a good quality in the track. May work easier for tracks made with quantization, so when the pattern of drums is consistent throughout the track. Also, you can use 4 stem Demucs ft or MDX23 and overlap drums from a fragment where you don’t hear vocals yet, so drums are still crispy there.
Ducking effect eliminator
You can also check Aufr33 Reaper 7.05 project aimed at alleviating this issue:
“the music volume is reduced where there are vocals”. Instruction:
“Just place two stems: vocals and music. Adjust the Expander if necessary.”
“It's just an expander side-chained to vocals. You can replicate this in any other DAW.”
- Nice chart (>moved to “Advanced chain processing chart” at the bottom of Karaoke section (use search)
describing process for creating AI cover (replace kim vocal with voc ft there, or MDX23 vocals/UVR top ensemble/Roformers).