Stain Acoustics: RT60 Meter

Stain Acoustics is an acoustic measurement and loudspeaker analysis tool for Android. Use your phone's microphone — or plug in a USB measurement mic with a .cal file — and get the numbers that matter: RT60, frequency response, harmonic distortion, and more, all computed from a single log-sweep recording.


WHAT'S INSIDE

Room Analyser
Measure reverberation time (RT60) using the ISO 3382 T20 method, clarity (C80), early decay time (EDT), definition (D50), signal-to-noise ratio, per-octave RT60, and the full frequency response. See the Schroeder decay curve on a tappable chart, compare octave bands side by side, and read interpretive notes on what the numbers mean for your room. Diagnostics flag room modes and speaker-boundary interference (SBIR) notches with predicted boundary distances.

Simple Sweep
A fast single-speaker test. Measure frequency response (with selectable 1/12, 1/6, 1/3 and 1/1 octave smoothing), harmonic distortion (THD plus H2, H3, H5), step response, impulse response, energy-time curve (ETC), waterfall (cumulative spectral decay), unwrapped phase, and group delay. Export results as FRD for XSim, VituixCAD, or any industry-standard crossover tool.

Speaker Lab
Build a library of speaker profiles and take multi-angle measurements (0°, ±15°, ±30°, ±45°...) to study directivity and off-axis response.

Sound Check
A calibrated C-weighted SPL meter (dB(C) per IEC 61672) with automatic level adjustment — finds the right playback volume for a sweep so you get a clean measurement every time.

Microphone calibration
Upload a .cal file for your USB measurement microphone; the sensitivity header is parsed automatically. No USB mic? Run the phone-microphone calibration wizard, which compares your phone against a USB reference and generates a correction curve. A manual sensitivity override is also available for users who can compare against a known SPL reference.

Recommended hardware
The Dayton Audio iMM-6C is a calibrated USB-C measurement microphone we recommend for accurate readings — drop in its .cal file and the app applies the per-unit correction automatically. The iMM-6C is one example among other calibrated USB measurement mics the app supports; any mic with a standard .cal file will work.

TECHNICAL DETAIL

• Farina exponential log-sine sweep (20 Hz – 20 kHz, 10 s, 48 kHz)
• Wiener-regularized frequency-domain deconvolution with SNR-adaptive regularization
• 1 kHz acoustic sync pulse + cross-correlation to eliminate Android, USB, and Bluetooth playback-latency jitter
• Zero-phase 2nd-order Butterworth bandpass per ISO octave band
• T20 RT60 estimation with T30 fallback (×3 / ×2 extrapolation)
• Schroeder backward integration
• Farina harmonic extraction from time-shifted echoes in the deconvolved impulse response
• C-weighting filter per IEC 61672, normalized to 0 dB at 1 kHz

Plays through the built-in speaker, 3.5 mm jack, USB DAC, or Bluetooth. Records through the phone mic or a USB audio interface using the Unprocessed input preset — AGC and noise-suppression are disabled.


BE REALISTIC ABOUT PHONE MICS

A phone microphone is not a measurement-grade instrument. For qualitative room diagnostics, A/B speaker comparisons, and setting playback levels it works well, especially after running the phone-mic calibration wizard. For quantitative work — reports, certifications, or any claim backed by numbers — plug in a proper USB measurement microphone with its .cal file.


PRIVACY

No ads. No analytics. No trackers. No network calls at all. Recordings and measurements stay on your device. The full privacy policy is linked on this Play Store listing.


ONE-TIME PURCHASE

Stain Acoustics is a paid app. No subscriptions, no in-app purchases, no ads — one price, all features unlocked.

COMING SOON

• Sub Crawl — optimal subwoofer placement via bass-only multi-point SPL minimization.

Questions or bug reports? Email sales@houseofstain.com — you'll reach me, the developer, directly.

Recent changes:
What's new in 1.7.0

Speaker Lab, built for crossover work:
• Full polar sets, fast — each angle after the first is one tap
• FRD exports carry true relative level, full resolution, honest headers
• VituixCAD-ready file names + impulse response WAV export for REW
• Harmonic curves and auto-scaling phase in every fresh session
• One clear chart style everywhere, labels in their own gutters

Calibration one tap away — the mic banner opens setup; uncalibrated readings link to MATCH REFERENCE.