To enable the Finder to show all files (including "hidden" ones), you can type the following command in at the command prompt in Terminal:
defaults write com.apple.Finder AppleShowAllFiles -bool YES; killall -HUP Finder
The first part sets a hidden preference so the finder shows all files; the second part restarts the Finder so these preferences take effect (killall on its own tells a program to quit; the -HUP flag asks the program to restart).
If you want to reverse this so that the Finder now hides the files it normally hides, type this in Terminal:
defaults write com.apple.Finder AppleShowAllFiles -bool NO; killall -HUP Finder
That said, your actual problem of disk space not being freed up when you "delete" files is actually by design.
To permanently delete a file, you need to empty the Trash — Mac OS X doesn't delete files directly in the Finder; it first moves them to a temporary storage on their original volume, and then when you Empty Trash… in Finder, the files get deleted.
Some users are reporting that defaults write com.apple.Finder is not working on their Mountain Lion systems but defaults write com.apple.finder (note the lower case) is working. On my system running Mountain Lion, I am finding that the command works as written, but if it doesn't for you, try lower-casing the F in Finder in defaults write statement.
If you just want to modify the saved search, copy it somewhere from /System/Library/CoreServices/Finder.app/Contents/Resources/CannedSearches/Today.cannedSearch, show package contents and open search.savedSearch in a text editor, and add this to the first RawQuery key:
&& kMDItemFSName != *.log && kMDItemFSName != *.upload && kMDItemFSName != *.json
You can drop it on the sidebar by holding command.
Best Answer
From within Finder, select the search box at the top right corner of the window and type Audio; a list will popup, near the bottom of which will be Kinds and Audio. Select that type, and then for the scope, select This Mac. This will show all the files on your Mac (at least within your Spotlight search's view) that OS X considers to be audio files.
You should be very cautious when deleting files shown this way, as you'll find many are embedded in applications, or used by other applications, including the OS, in various ways; deleting them may render an application dysfunctional.