cheezmo said:More sound quality improvement would come from increasing the encoding bitrate to 160kbps or 192kbps than from changing the sampling frequency. 128kbps AAC falls so far short of CD quality as it is that working on getting closer to CD quality would be the first step.
Yes, this is true. Everybody should listen to cheezmo and then google a site for digital signal processing.
The human ear an only hear frequencies as high at 20 kHz. when converting an analog signal to a digital signal, the converter samples the signal at a certain rate (that is to say, it pick spots along the waveform and digitizes those spots). Now, for in interest of storage space and minimizing overkill, 44 kHz sampling is the perfect rate at which to convert a music file as you won't lose any frequency due to the nyquist effect (see: http://ei.cs.vt.edu/~netinfo/notes/chap1/digitalsound/sampling.html ).
the best thing to do to increase quality of conversion is to increase the depth of the sample, that is, bits per sample... subsequently leading to increases bits per second.