Enum rubato::InterpolationType

pub enum InterpolationType {
    Cubic,
    Linear,
    Nearest,
}

Interpolation methods that can be selected. For asynchronous interpolation where the ratio between input and output sample rates can be any number, it’s not possible to pre-calculate all the needed interpolation filters. Instead they have to be computed as needed, which becomes impractical since the sincs are very expensive to generate in terms of cpu time. It’s more efficient to combine the sinc filters with some other interpolation technique. Then sinc filters are used to provide a fixed number of interpolated points between input samples, and then the new value is calculated by interpolation between those points.

Variants

Cubic

For cubic interpolation, the four nearest intermediate points are calculated using sinc interpolation. Then a cubic polynomial is fitted to these points, and is then used to calculate the new sample value. The computation time as about twice the one for linear interpolation, but it requires much fewer intermediate points for a good result.

Linear

With linear interpolation the new sample value is calculated by linear interpolation between the two nearest points. This requires two intermediate points to be calculated using sinc interpolation, and te output is a weighted average of these two. This is relatively fast, but needs a large number of intermediate points to push the resampling artefacts below the noise floor.

Nearest

The Nearest mode doesn’t do any interpolation, but simply picks the nearest intermediate point. This is useful when the nearest point is actually the correct one, for example when upsampling by a factor 2, like 48kHz->96kHz. Then setting the oversampling_factor to 2, and using Nearest mode, no unnecessary computations are performed and the result is the same as for synchronous resampling. This also works for other ratios that can be expressed by a fraction. For 44.1kHz -> 48 kHz, setting oversampling_factor to 160 gives the desired result (since 48kHz = 160/147 * 44.1kHz).

Trait Implementations

impl Debug for InterpolationType

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.