Documentation sections

I2S Audio Interface Timing Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug i2s-timing. Calculate I2S bit clock (BCLK), word clock (LRCLK/WCLK), and data rate for audio interfaces at any sample rate, bit depth, and channel count.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of i2s-timing
Name	Unit	Range	Default	Description
sampleRatenumber	kHz	0.1 … 768	44.1	Audio sample rate (e.g., 44.1, 48, 96, 192 kHz)
bitDepthnumber	bits	8 … 64	24	Bits per sample (common: 16, 24, 32 bits)
channelsnumber	none	1 … 32	2	Number of audio channels (1 for mono, 2 for stereo)
mclknumber	MHz	0.1 … 200	16.9344	The clock BCLK is divided from by a whole number: 16.9344 MHz is 384 × 44.1 kHz, 12.288 MHz is 256 × 48 kHz
rateBudgetnumber	%	0.001 … 10	0.1	The sample-rate error the link can take; ±0.1 % (1000 ppm) is IEC 60958-3's Level II clock accuracy for consumer digital audio

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of i2s-timing
Field	Unit	Description
bclkheadline	MHz	Bit clock frequency: BCLK = Fs × bit_depth × channels
wclk	kHz	Word/frame clock frequency = sample rate
bclkPeriod	ns	Period of one BCLK cycle
dataRate	Mbps	Raw audio data rate on the I2S bus
mclkDivider	none	The whole number MCLK is divided by, the nearest to MCLK/BCLK
bclkActual	MHz	MCLK over the divider
sampleRateActual	kHz	The actual BCLK over the bits in a frame
sampleRateError_pct	%	Actual over requested, signed; zero only where MCLK is a whole multiple of BCLK

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "i2s-timing",
    "inputs": {
      "sampleRate": 44.1,
      "bitDepth": 24,
      "channels": 2,
      "mclk": 16.9344,
      "rateBudget": 0.1
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("i2s-timing", {
    "sampleRate": 44.1,
    "bitDepth": 24,
    "channels": 2,
    "mclk": 16.9344,
    "rateBudget": 0.1,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "i2s-timing",
    "inputs": {
      "sampleRate": 44.1,
      "bitDepth": 24,
      "channels": 2,
      "mclk": 16.9344,
      "rateBudget": 0.1
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "i2s-timing",
	  "inputs": {
	    "sampleRate": 44.1,
	    "bitDepth": 24,
	    "channels": 2,
	    "mclk": 16.9344,
	    "rateBudget": 0.1
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "i2s-timing",
  "values": {
    "bclk": 2.1168,
    "wclk": 44.1,
    "bclkPeriod": 472.411186696901,
    "dataRate": 2.1168,
    "mclkDivider": 8,
    "bclkActual": 2.1168,
    "sampleRateActual": 44.1,
    "sampleRateError_pct": 0
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:i2s-timing",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Philips I2S Bus Specification, 1996",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "sampleRate": {
          "min": 0.1,
          "max": 768,
          "unit": "kHz"
        },
        "bitDepth": {
          "min": 8,
          "max": 64,
          "unit": "bits"
        },
        "channels": {
          "min": 1,
          "max": 32,
          "unit": ""
        },
        "mclk": {
          "min": 0.1,
          "max": 200,
          "unit": "MHz"
        },
        "rateBudget": {
          "min": 0.001,
          "max": 10,
          "unit": "%"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "sampleRate": 44.1,
      "bitDepth": 24,
      "channels": 2,
      "mclk": 16.9344,
      "rateBudget": 0.1
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "sampleRate"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageI2S Audio Interface Timing Calculator, at these values