Absolutely a bad idea!!!! DON'T Upsample Your Music Files!
I cant emphasize this enough! Don't do it! Don't do it! Don't do it!
Fixed-point upsampling will create distortion whenever an intersample peak exceeding 0 dBFS occurs. This distortion is often audible because it is quite severe when it occurs. On many CD recordings, this can occur multiple times per second.
See my whitepaper on this topic here:
Intersample Overs in CD Recordings
Intersample peaks can reach +3.01 dBFS. Recordings that are not overly compressed, or overly loud, may contain more intersample overs than recordings that are mastered for maximum loudness. In other words, your best recordings may sustain the highest damage from upsampling the files.
If a DAC is properly designed (with enough DSP headroom and enough analog headroom), the intersample peaks exceeding 0 dBFS can be rendered without distortion. Please note that most DACs clip intersample peaks because they do not have any headroom above 0 dBFS. When this clipping occurs, it is not harmonic distortion. Instead, each clip produces a burst of broadband noise. In other words, you will hear short percussive bursts of noise at every occurrence of an overload. This is not like the sound of an amplifier clipping. It may correspond to the beat of the music and may be mistaken for a percussion instrument, but it is a sound that was not in the original recording. This percussive noise artifact is easy to hear once you learn what to listen for.
Upsampling can be done without causing damage if the audio level is reduced by at least 3 dB
before upsampling. We do this within our Benchmark DAC2 and DAC3 converters. It can also be done correctly within a floating point environment, but again the level will need to be reduced by at least 3 dB before saving it back to a fixed point format. For a variety of very good reasons, music recordings are only distributed in fixed-point formats. If you upsample these without a level reduction, you will do permanent damage.
Fixed-point to fixed-point upsampling "bakes" intersample DSP overloads into the upsampled product. This distortion is audible and it cannot be removed. Upsampling will damage the sound of your recordings unless you reduce the signal level.
Beware of upsampled versions of 44.1 kHz recordings. These usually have baked-in distortion. Find the 44.1/16 originals.
Unfortunately some online music services provide "high-resolution" versions of 44.1 kHz recordings that have been upsampled directly from the 44.1 kHz originals without reducing the level. Avoid these "high-resolution" versions.
