Audio samples are processed with the highest precision (64-bit float) and with the most accurate algorithms for the best audio quality.
Audio Engine uses very high quality SoX resampler. See information about the SoX resampler at SoX - Sound eXchange | Resampling.
SoX resampler is the default sample rate converter in all conversions. SoX resampler is also used with the Opus and MP3 encoders that usually use their own built-in resamplers. SoX resampler provides better audio quality than the built-in resamplers.
Resampler's passband setting determines how much of the frequency content of the original signal (wrt the original sample rate when up-sampling, or the new sample rate when down-sampling) is preserved during conversion. The term 'passband' is used to refer to all frequencies up to the bandwidth point (e.g. for 44.1kHz sampling rate, and a resampling passband of 95%, the passband represents frequencies from 0Hz to ~21kHz). Increasing the resampler's passband results in a slower conversion and can increase transient echo artefacts.
Default sweep 95% - Conversion from 96kHz to 44.1kHz
Default passband 95% - Conversion from 96kHz to 44.1kHz
Steep sweep 99% - Conversion from 96kHz to 44.1kHz
Steep passband 99% - Conversion from 96kHz to 44.1kHz
Aliasing above the passband is allowed. For example, with 44.1kHz sampling rate, and a resampling passband of 95%, this means that frequency content above ~21kHz can be distorted; however, since this is above the passband (i.e. above the highest frequency of interest/audibility), this may not be a problem. The benefits of allowing aliasing are reduced processing time, and reduced (by almost half) transient echo artefacts.
Default sweep 95%, aliasing allowed - Conversion from 96kHz to 44.1kHz
Default passband 95%, aliasing allowed - Conversion from 96kHz to 44.1kHz
Steep sweep 99%, aliasing allowed - Conversion from 96kHz to 44.1kHz
Steep passband 99%, aliasing allowed - Conversion from 96kHz to 44.1kHz
If EZ CD Audio Converter needs to reduce the bit depth, then there will be rounding errors. If each sample value is rounded to the nearest (24-bit, 16-bit, or 8-bit) value, then the steppiness in the output may be audible, especially with extremely quiet sounds. EZ CD Audio Converter can apply Dither in the conversion to avoid this - it is often compared to graphics' Anti-Aliasing that is used to smooth the steppiness of edges. Rather than always rounding to the nearest value, dithering will apply a degree of randomness to the rounding to prevent steppiness.
Dither will be applied (when enabled from the Settings) if converting from ORIGINAL source of
· 64-bit, 64-bit float, 32-bit, 32-bit float to 24-bit
· 64-bit, 64-bit float, 32-bit, 32-bit float, 24-bit to 16-bit
· 64-bit, 64-bit float, 32-bit, 32-bit float, 24-bit, 16-bit to 8-bit
Noise-shaped dither has a higher peak amplitude than other forms of dither, but the noise is concentrated in the very high frequency range where it is less audible. Noise-shaped dither implements Lipshitz minimally audible noise shaping.
Triangular dither produces a lower peak amplitude of noise than Noise-shaped, but the noise is concentrated less in the higher frequencies.
Rectangular dither produces a similar noise amplitude as triangular, but with very small amounts of randomization. The frequency distribution is fairly even, such that it approximates white noise. Unlike the other two forms of dither, rectangular does not add noise to absolute silence.