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Butterworth Filter API

healthy 3,767 Subscribers

Butterworth-filter design maths as an API, computed locally and deterministically. The order endpoint computes the minimum filter order needed to meet a specification — from the passband edge frequency and its allowed ripple and the stopband edge frequency and its required attenuation it returns the exact and rounded-up order, n = ⌈log10((10^(As/10)−1)/(10^(Ap/10)−1)) / (2·log10(fs/fp))⌉, where each extra order adds 20 dB per decade of roll-off. The response endpoint computes the maximally-flat magnitude response of an n-th order Butterworth filter at a frequency, |H| = 1/√(1 + (f/fc)^(2n)), in linear and decibel form with the attenuation and the asymptotic roll-off — the response is exactly −3.01 dB at the cutoff for any order. The poles endpoint gives the s-plane pole locations, equally spaced on a circle of radius ωc in the left half-plane at angles π·(2k+n−1)/(2n), all stable. Frequencies are in hertz (or any consistent unit), ripple and attenuation in decibels and the order a positive integer. Everything is computed locally and deterministically, so it is instant and private. Ideal for DSP, audio, RF, instrumentation and embedded app developers, anti-aliasing and filter-design tools, and signal-processing education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is the Butterworth filter; for a single-pole RC cutoff and resonance use a resonance API and for AC impedance an impedance API.

#butterworth #filter #dsp #signal-processing #electronics #developer-tools
api.oanor.com/butterworth-api
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Machine-readable spec so AI agents can integrate this API.

/api/butterworth-api/openapi.json
/api/butterworth-api/llms.txt

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API health

healthy
Uptime
100.00%
Server probes · 24h
Avg latency
83 ms
Server probes · 24h
Subscribers
3,767
active
Total calls
8
last 7 days
status Full status page → · 12 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

Free

  • 2,900 calls / month
  • 2 requests / second
  • Hard cap (429 above quota, no overage)
  • 2,900 calls/month
  • 2 req/sec
  • Order + response + poles
  • No credit card
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Starter

€9.00 /month

  • 40,000 calls / month
  • 6 requests / second
  • Hard cap (429 above quota, no overage)
  • 40,000 calls/month
  • 6 req/sec
  • Spec-driven order, dB response
  • Email support
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Pro

€24.00 /month

  • 250,000 calls / month
  • 15 requests / second
  • Hard cap (429 above quota, no overage)
  • 250,000 calls/month
  • 15 req/sec
  • DSP & audio-filter pipelines
  • Priority support
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Mega

€72.00 /month

  • 1,690,000 calls / month
  • 40 requests / second
  • Hard cap (429 above quota, no overage)
  • 1,690,000 calls/month
  • 40 req/sec
  • Platform scale
  • Dedicated SLA
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Related APIs

Other APIs with overlapping tags.

Chebyshev Filter API

Chebyshev Type I filter-design maths as an API, computed locally and deterministically. The order endpoint computes the minimum filter order to meet a specification, n = ⌈acosh(√((10^(As/10)−1)/(10^(Ap/10)−1))) / acosh(fs/fp)⌉, from the passband edge frequency and its ripple and the stopband edge and its required attenuation — a Chebyshev filter usually needs a lower order than a Butterworth for the same specification, trading a flat passband for equiripple. The response endpoint computes the equiripple magnitude response, |H| = 1/√(1 + ε²·Tₙ²(f/fc)) with the ripple factor ε = √(10^(Ap/10) − 1) and the Chebyshev polynomial Tₙ, in linear and decibel form — in the passband the magnitude ripples between 0 and −Ap dB and reaches exactly −Ap dB at the cutoff, then rolls off faster than a Butterworth. The ripple endpoint converts between the passband ripple in decibels and the ripple factor ε, with the passband maximum and minimum. Frequencies are in hertz, ripple and attenuation in decibels and the order a positive integer. Everything is computed locally and deterministically, so it is instant and private. Ideal for DSP, audio, RF, communications and instrumentation app developers, filter-design and selectivity tools, and signal-processing education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is the Chebyshev Type I filter; for the maximally-flat Butterworth use a Butterworth API.

api.oanor.com/chebyshev-api

CSV API

A fast, fully-local CSV data toolkit: parse CSV into typed row objects (RFC-4180), compute per-column statistics (count, unique, type and top values, and for numeric columns min, max, mean, median and sum), remove duplicate rows by all or a subset of columns, sort by a column with numeric-aware ordering, and filter rows by a condition (equals, not-equals, greater/less than, contains, starts-with, empty, not-empty). Every endpoint accepts input via the query string or the request body, up to 2 MB, and returns both row objects and a CSV string. Pure server-side compute, no third-party upstream, so responses are instant and always available. Ideal for data wrangling, ETL, analytics preparation, spreadsheet tooling and data cleaning. (For plain CSV to JSON conversion, see the oanor JSON API.)

api.oanor.com/csv-api

ADC & DAC Converter API

ADC/DAC data-converter maths as an API, computed locally and deterministically. The resolution endpoint turns a bit depth into the number of quantization levels (2^N), the LSB step for a given reference voltage (in V, mV and µV), the full-scale range, the ideal signal-to-noise ratio (6.02·N + 1.76 dB) and dynamic range, and — given an input voltage — the digital output code. The sampling endpoint covers Nyquist: the minimum sample rate for a signal bandwidth (2·f_max), the Nyquist frequency for a sample rate (fs/2), whether a signal is adequately sampled, and the alias frequency a tone folds to, |f_in − round(f_in/fs)·fs|. The quantization endpoint gives the maximum quantization error (LSB/2), the rms quantization noise (LSB/√12), the ideal SNR, and the effective number of bits (ENOB = (SNR − 1.76)/6.02) from a measured SNR. Everything is computed locally and deterministically, so it is instant and private. Ideal for embedded, DSP, audio and instrumentation app developers, data-acquisition and converter-selection tools, and electronics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is data-converter & sampling maths; for media bitrate and file size use a bitrate API and for AC reactance and resonance use a resonance API.

api.oanor.com/adc-api

Voltage Divider API

Resistive voltage-divider circuit design as an API, computed locally and deterministically. The divide endpoint takes an input voltage and two resistors and returns the output voltage Vout = Vin·R2/(R1+R2), the current I = Vin/(R1+R2) that flows through the chain, and the power dissipated in each resistor and in total — a 12 V source with R1 = 1 kΩ and R2 = 2 kΩ gives 8 V at 4 mA. The loaded endpoint adds a load resistor across R2, computes the parallel combination R2′ = R2·RL/(R2+RL) and the loaded output Vout = Vin·R2′/(R1+R2′), and reports the droop in volts and percent against the unloaded value, the classic mistake when a divider feeds a real load. The resistor endpoint sizes the missing resistor for a target output — R2 = R1·Vout/(Vin−Vout) or R1 = R2·(Vin−Vout)/Vout — so you can pick parts for a reference or sensor-bias point. All quantities are volts, ohms, amps and watts. Everything is computed locally and deterministically, so it is instant and private. Ideal for electronics, embedded, hardware, sensor-interfacing and EE-education app developers, reference-voltage and bias-network tools, and maker software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is the resistive divider; for a single Ohm’s-law relationship use an Ohm’s-law API and for RC/RL filters an RC-filter API.

api.oanor.com/voltagedivider-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Butterworth Filter API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Butterworth Filter API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Butterworth Filter API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Butterworth Filter API cost?
Butterworth Filter API has a free tier with 100 calls / month. Paid plans start at €9.00 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Butterworth Filter API GDPR-compliant?
All requests to Butterworth Filter API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.

Pick an endpoint from the list on the left to see its details and try it.

Code snippets

Sign up to get an API key, then call any path under your slug.

curl https://api.oanor.com/butterworth-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."
const res = await fetch("https://api.oanor.com/butterworth-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();
$ch = curl_init("https://api.oanor.com/butterworth-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);
import requests
r = requests.get(
    "https://api.oanor.com/butterworth-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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