Measurement setup — input channel, calibration, test tone

Setup (next to the Ring-out · Level · Transfer tabs) holds everything a measurement needs before it starts: which input channel the mic is on, how that mic and that channel are calibrated, and a test tone. Ring-out, Level and Transfer all read the same measurement channel.

Input channel

1. Tap Start listening (or the button in Setup) so the browser opens the input.
2. Setup lists every channel the browser passes, each with a live meter — peak and RMS in dB FS. Talk into the measurement mic or scratch its grille: the channel that moves is the one to pick.
3. Tap that channel. It becomes the measurement channel at once; ring-out starts its detection over on it.

The choice is remembered for this input, on this device — it is never synced to your account, like the input itself.

How many channels you see depends on the browser. SpectraSense asks for every channel and shows what really arrives. Chrome and Edge pass all inputs of a multichannel interface. Safari and Firefox often pass only the first one or two — Setup says so. If your mic is on input 5 and you only see two channels, use Chrome or Edge, or repatch the mic to input 1 or 2.

Mic calibration file

A measurement mic comes with a calibration file: its own deviation from flat, frequency by frequency. Load it with Load calibration file; the spectrum is then corrected for it (detection always reads the uncorrected signal).

• Formats: miniDSP UMIK-1 and UMIK-2 files (with their "Sens Factor =…dB, SERNO: …" first line), REW calibration files, and plain two-column text — frequency in Hz and deviation in dB, separated by spaces, tabs, commas or semicolons (a decimal comma works with semicolons or tabs). Lines starting with *, # or " are comments.
• Checks: frequencies must rise from line to line and stay within 10 Hz – 24 kHz, deviations within ±30 dB, at most 2,000 lines and 200 kB. A file that fails says which line.
• 0° or 90°: miniDSP ships two files. Use the 0° file when the mic points at the source (a speaker, on axis). Use the 90° file when the mic points straight up at the ceiling — the usual way to measure a room or a system from the audience position.
• Setup shows the active file: its name, the serial number and the number of points. Remove switches the correction off.

The file's Sens Factor is shown, but it does not set the SPL — an interface's input gain changes that. Calibrate SPL as below.

SPL calibration

Readings are in dB FS — relative to the input's full scale — until the channel is calibrated; uncalibrated readings are always labelled "dB FS (uncalibrated)". A calibration stores one offset (dB SPL − dB FS) for this input and this channel, with its date. Change the input gain afterwards and the calibration is wrong — calibrate again.

With a calibrator (best):

1. Pick the measurement channel and set the input gain as you will measure.
2. Fit the calibrator snugly on the mic and switch it on.
3. Choose its level — 94 or 114 dB SPL at 1 kHz — and tap Measure (3 s).

SpectraSense measures the 1 kHz band for three seconds. It refuses if the input clips, if there is hardly anything on the channel, or if the 1 kHz tone does not carry the level (calibrator not seated, not switched on, or the room is louder).

Against a reference meter:

1. Play pink noise from the test tone (below) through the system, well above the room noise.
2. Hold a sound level meter next to the mic, set to C or Z weighting, slow.
3. Type its reading and tap Measure (3 s).

This is only as good as the meter, and the two must stand at the same spot.

Profile file

Calibration stays in this browser: it belongs to one mic on one interface. Export profile saves the mic file and every SPL calibration as a small file; Import profile on another computer (or after clearing the browser) brings them back and replaces what that browser had.

Test tone

Pink noise, white noise, a sine or a log sweep, for calibrating, checking a system, or (in Transfer) as the reference.

• It never starts by itself and always starts at −40 dB FS. The level is the signal's peak level; the RMS is shown next to it (pink noise sits about 13 dB lower).
• Level changes and Stop fade — no click.
• The level stops at −6 dB FS. Allow up to 0 dB FS lifts that — pull the system fader down first; a full-scale test tone can damage drivers and ears. Unticking it brings a hotter level back to −6.
• Output: Chrome and Edge let you pick the output device. Other browsers play through the system output — choose it in the system's sound settings.
• While a tone plays, a bar with a big Stop stays at the top of the page on every tab.
• Sent vs. heard: next to the level sent, Setup shows what the measurement channel hears — in dB SPL once that channel is calibrated, otherwise in dB FS (uncalibrated). The difference is the gain from the output to the listening position.

Pink noise here is periodic (it repeats every few seconds with no seam) and has nothing below 10 Hz, so it is gentle on speakers and steady on a meter.

Good to know

• Nothing in this setup is synced to your account and nothing is uploaded: the channel choice, the calibration and the output stay on this device.
• Bluetooth outputs add delay and processing — fine for listening, not for measuring.
• A phone's built-in microphone is not a measurement mic: its levels are indicative only, calibrated or not.