It always bothered me that, whereas analog recordings strive to minimize added noise, digital recordings purposely add noise. It’s called dither. They say it is necessary and can’t be removed. It is used to mask quantization noise. Quantization noise is strongly correlated with the signal which makes it plainly audible in certain circumstances, such as listening to computer generated test tones. However, with recorded acoustic instruments and voices, the ambient noise in the venue and the self-noise of the microphones and electronics leading up to the A/D is usually sufficient to decorrelate the quantization noise.
Up-Down Sampling (UDS) removes dither noise, which, in my system, manifests as a gritty sound from the tweeter. I initially implemented UDS using Foobar and two instances of a resampler plugin. The first instance resampled to a high multiple of the CD rate, e.g. 2.8224M. The second instance resampled that output to a rate my DAC accepted, e.g. 176.4K. The process worked better than expected. I now use a custom libsoxr plugin that up-samples to as high as 45.1584M and then down-samples to 176.4K.
Up-sampling interpolates new samples which are inserted between the existing samples. Down-sampling uses a low-pass filter to remove the audio spectra above the Nyquist frequency before decimating. That spectrum includes the dither.
Up-Down Sampling (UDS) removes dither noise, which, in my system, manifests as a gritty sound from the tweeter. I initially implemented UDS using Foobar and two instances of a resampler plugin. The first instance resampled to a high multiple of the CD rate, e.g. 2.8224M. The second instance resampled that output to a rate my DAC accepted, e.g. 176.4K. The process worked better than expected. I now use a custom libsoxr plugin that up-samples to as high as 45.1584M and then down-samples to 176.4K.
Up-sampling interpolates new samples which are inserted between the existing samples. Down-sampling uses a low-pass filter to remove the audio spectra above the Nyquist frequency before decimating. That spectrum includes the dither.