Upsampling Test:

Test was performed using SoundForge 9.0:

A 5kHz test tone was created using the synthesis tool in SoundForge at 44.1k 24 bit. Original waveform is shown in the following graph:

Figure 1: Original Test Tone

Using an iZotope limiter plug-in, the tone was then highly limited in order to create harmonic distortion. Figure 2 shows the plug-in settings while Figure 3 shows the resulting graph after processing. This graph shows significant harmonic distortion and alias frequencies below 5kHz.

Figure 2: Limiter Settings

Figure 3: Test Tone after processing at 44.1k

The original test tone was then upsampled to 96kHz using SoundForge and processed with the same limiter setting as above. From the graph in figure 4 it can be seen that while harmonic distortion and alias frequencies are still present, they are not to the degree as when processed at a 44.1k sample rate, as well as not having alias frequencies to any measurable degree below 1kHz.

Figure 4: Original test tone upsampled to 96kHz and processed

The processed 96k tone was then downsampled using SoundForge to 44.1k with an anti-alias filter. The graph in Figure 5 shows the harmonic distortion is well below that of the original file processed at the 44.1k sample rate. There are also still no measurable alias frequencies below 1kHz.

Figure 5: Downsampled processed 96k file