Need to strip the beginning ./ characters in a function

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for f in ./*.mp3; do sox "$f" "${f%%.mp3}processed.mp3" silence 1 0.02 1% -1 0.02 1%; done

This is a script I'm using to process audio files. The problem is that it keeps going in a loop, processing the new audio files as well. I'd like to fix this by having the output go in a subfolder, so I tried this:

for f in ./*.mp3; do sox "$f" "/subfolder${f%%.mp3}processed.mp3" silence 1 0.02 1% -1 0.02 1%; done

This is the output:

/subfolder./01processed.mp3

This is giving me an error with SoX, I need to remove the ./ before the filename output, how might I do that? This is the output I'd like to have:

/subfolder/01processed.mp3

What I have tried:

I tried indicating a subfolder, but I can't seem to remove the leading ./ from the filename, and that's making SoX crash.