"Why does it happen and how I can fix this?"
Because [] is a concatenation operator, not a list operator as some beginners imagine. So your line
filename = ['asr','cnn','dnn','hmm','tts'];
is exactly equivalent to this:
filename = 'asrcnndnnhmmtts';
which is not very useful in your situation. Then inside the loop you simply access one of those characters using indexing:
filename(1,i) % get ONE character
You can fix this trivially by using a cell array to store those character vectors, but this does not resolve that fact that your code is vary badly designed: using eval to access variable names is one way that beginners force themselves into writing slow, complex, buggy code that is hard to debug. Read this to know why:
"I already have matrices like asr1, asr2... in the workspace."
DO NOT DO THIS! Magically accessing variable names is a bad way to write code. Presumably you did not sit and write out lots of variable name by hand, so they must have been imported/generated somehow, and that is exactly where you should FIX your badly designed code. For example, instead of load-ing directly into the workspace, you should load into an output variable (which is a structure):
S = load(...)
If you explain how those variables came into the workspace, we can show you better ways to write your code.
