How to get an incremental letter

I want to insert a lowercase letter as the fourth character in a list of filenames. I thought I put the right string in, but it just gives me the same letter (in this case 'a') over and over again. I want the letter to increase by one for each file. So track 2 should have a 'b', track 3 a 'c', ect.

This is what I used: A1.$char($add($num(%1,1),97)) %2

The lowercase letter comes after A1.

The 97 indicates the lowercase 'a', but what am I not doing right to get that letter to increase for each file?

You could try it with
A1.$char($add($num(%TRACK%,1),97))
you should replace %2 with the content of another tag like %TITLE% or %ARTIST%.
This would produce
A1.b
A1.c
A1.d

If you want to start with the lowercase letter a, you should start with the value 96 instead of 97.

It still gives me the same repeated character. Also I need to use %2 because it retains the remainder of the filename.

I can't help you further, unfortunately.

In my test, I load 3 tracks, choose Tag -> Tag for _FILENAME and use the above format string and it works as expected.

As said, I don't have your %2 as I don't see how this could work and where the content should come from. But it does not repeat the same character. It start at a over b to c If I use 96 instead of 97.

You would have to supply the original filename, the pattern you used for the original filename and the pattern for the target filename.
If A1 is the %1 part, then $num(%1,1) will always return 0 as value.

Okay, I see part of the problem. I wasn't doing it in Tag - Tag. I was doing it in Filename - Filename. The %1, %2 ect. values don't work in Tag - Tag, do they?

I should've mentioned which conversion section I was using. I used your code in Tag - Tag and added %TITLE% and got the result I needed. Thank you.

The original filenames are:
A1 Computaform
A2 Computaform
A3 Computaform
A4 Computaform

But I wanted all of those files to start with A1. followed by an incremental letter. So they would end up like this:

A1.a Computaform
A1.b Computaform
A1.c Computaform
A1.d Computaform

So the "A1." was manually typed in by me. I just needed the rest of the string to make the lowercase letter adjust incrementally.

My issue was trying it in Filename - Filename, when I should've done it in Tag - Tag.