I build guitartuner successfully on earlier version of QtCreator.
Recently upgraded to 4.7.4 on both Windows and Linux (Fedora Core 14).

Both fail to build (there is an existing issue raised for NT)

On Linux, when you load the guitar tuner app up from the Qt Welcome screen (search guitar in demos search) the build fails.
Complains lack of QAudioDeviceInfo, QAudioOutput and QAudioInput lines 46 - 48 of guitartuner.h

I found these files, and realized if I modify the guitartuner.pro as follows, it builds. But the include files are still highlighted with an underscore.

#-------------------------------------------------
#

1. Project created by QtCreator 2010-10-22T14:28:56
   #
   #-------------------------------------------------

--QT += core gui
++QT += core gui multimedia