Interpolation Rate Calculator

Summary

Enter an input sample rate and target output sample rate to compute the integer interpolation factor L and verify the resulting output rate.

How it works

1. Enter the input sample rate (Fin) in Hz — for example 44100 for CD audio.
2. Enter the desired output sample rate (Fout) in Hz — for example 48000.
3. The calculator finds GCD(Fin, Fout) and reduces the ratio Fout/Fin to lowest terms L/M.
4. L is the interpolation (upsampling) factor; M is the decimation (downsampling) factor.
5. The intermediate rate after upsampling equals Fin × L; the final rate after decimation equals Fin × L / M.
6. If L = 1, no upsampling is needed; if M = 1, no decimation is needed (pure interpolation).

Use cases

• Determine L and M for a polyphase sample rate converter between two audio standards.
• Plan the intermediate buffer size when upsampling before decimation in a DSP chain.
• Verify that two sample rates share a common integer ratio before designing a filter bank.
• Check whether a simple integer-L FIR upsample is sufficient or a rational L/M SRC is needed.
• Calculate the anti-imaging filter cutoff relative to the interpolated rate.
• Compare multiple target rates to find the one requiring the lowest L for hardware cost.

Frequently Asked Questions