Calibration

Calibration establishes the true sensitivity of a measurement chain — microphone, cable, input conditioning and analog-to-digital conversion together — by measuring a known reference. Deepsona provides a pistonphone calibration wizard for sound pressure channels, and a separate playback SPL calibration for listening to and analysing recordings.

When to Calibrate

Before any measurement whose absolute level matters (sound pressure level, sound power, psychoacoustic metrics).
After changing the microphone, the preamplifier, the cable or the input channel.
After changing the input Range, Supply or Highpass of the channel — these are part of the chain the calibration measures.
At the start and, for critical measurements, at the end of a measurement session, so that any drift is detected.
When the sensitivity you have is only a nominal data-sheet value and you need a traceable figure.

If your sensor carries a TEDS chip, reading TEDS already gives you the manufacturer's calibrated sensitivity and may be sufficient. Pistonphone calibration additionally accounts for the cable and the input conditioning of the specific channel you are using.

Prerequisites

A sound calibrator or pistonphone with a known output level.
The frontend selected and the microphone connected to the channel you intend to calibrate.
The channel's Supply, Range and Highpass already set to the values you will use for the measurement.
A running Preview. The calibration dialog reads the live signal — it starts Preview for you if the recorder is idle, and stops it again when you close the dialog.

Calibrate with the settings you will actually measure with. Changing the input range after calibrating invalidates the result — the sensitivity you captured belongs to that specific chain configuration.

Pistonphone Calibration Procedure

Open the Recorder Configuration tab.
In the row of the microphone channel, click the second small button in the Sensitivity cell — tooltip Calibration. The Pistonphone Calibration dialog opens with that channel preselected.
Check the Channel selection. Only analog channels are offered.
Choose the Reference level that matches your calibrator.
Fit the calibrator onto the microphone and switch it on. Make sure it is seated properly and that the environment is quiet.
Watch the Live RMS read-out. Wait about 3 seconds for it to settle — the status line prompts: "Hold pistonphone on microphone. Wait ~3 s for the RMS reading to stabilize, then click Capture."
Click Capture. The value is frozen in the Captured field and the Computed sensitivity panel shows the result in mV/Pa.
Click Apply. The sensitivity is written into the channel row and the unit is set to Pa. The dialog closes.
Remove the calibrator and confirm in the Online Monitor that the channel now reads a plausible sound pressure level.

The dialog reads the live level five times per second, so the Live RMS display responds immediately when you fit or remove the calibrator. Values are auto-scaled: volts above 1 V, millivolts above 1 mV, microvolts below that.

Changing the Reference level after capturing recomputes the sensitivity from the same captured reading — you do not have to capture again. Changing the Channel, however, clears the capture and you must measure again.

Reference Levels

Two standard reference levels are offered. Pick the one printed on your calibrator.

Reference level	Sound pressure	Typical instruments
94 dB SPL @ 1 kHz	1 Pa	Sound level calibrators (e.g. B&K 4231, GRAS 42AB)
114 dB SPL @ 250 Hz	10 Pa	Pistonphones (e.g. B&K 4220)

The frequency is informational and does not enter the calculation. What matters is that the sound pressure level produced by your calibrator matches the level you select.

Selecting the wrong reference level produces a sensitivity that is wrong by a factor of ten. If a calibrated channel reads exactly 20 dB too high or too low, this is the first thing to check.

How the Sensitivity Is Computed

The reference level is converted to a sound pressure in pascals, and the captured RMS voltage is divided by it:

p_ref = 10^{(L_ref − 94) / 20} Pa S = U_RMS × 1000 / p_ref mV/Pa

So 94 dB corresponds to 1 Pa and 114 dB to 10 Pa. A microphone that produces 50 mV RMS in a 94 dB calibrator has a sensitivity of 50 mV/Pa.

The result is the sensitivity of the whole chain. If it differs noticeably from the microphone's data-sheet value, the difference is in the cable, the preamplifier or the input conditioning — which is exactly what calibration is meant to capture.

Storing and Reusing Calibration Values

A calibration result lives in the channel row. From there it is preserved in three ways:

Where	What is kept	How to reuse it
Channel settings file (`.vlcs`)	Sensitivity, unit and the rest of the channel table.	Save channel settings to a .vlcs file, then import it at the start of the next session with the same frontend.
Recording metadata	Sensitivity, sensitivity unit, output unit, sensor identity and calibration date are written into every `.dpsa` recording.	Automatic. Engineering-unit scaling is applied from this metadata when the recording is analysed.
Sensor Library	Nominal and calibrated sensitivity per channel plus a dated calibration history.	Enter the calibrated value in the sensor's Calibrated Sensitivity field and add a Calibration History entry. Assign that sensor to a channel to reuse it.

Because samples are stored as voltage and the sensitivity travels as metadata, a calibration you correct later can be applied to an existing recording without re-measuring. Recording first and calibrating afterwards is possible — but calibrating first is safer, because it lets you verify the levels before you commit to a measurement.

The pistonphone dialog writes to the channel row only. It does not add an entry to the Sensor Library automatically. If you want a permanent, dated record of the calibration, enter it in the Sensor Library yourself.

Playback SPL Calibration

A separate calibration governs how an existing recording is interpreted for playback and level analysis. It is set in the toolbar strip labelled SPL Calib:, which defines what a full-scale sample corresponds to in dB SPL.

Field	Meaning	Default
`FS=` … dB SPL	The sound pressure level, in dB SPL peak, that a full-scale sample represents.	114.0
`Sens=` … mV/Pa	Sensor sensitivity. A typical 1/4" microphone is around 50 mV/Pa. Enter 0 if not used.	0
`Gain=` … dB	Upstream signal-chain gain such as a preamplifier. Enter 0 for none.	0

The summary line next to the fields confirms the current setting, for example 1.0 PCM = 114.0 dB SPL peak · sens 50.0 mV/Pa.

This calibration is stored per source file and is restored automatically the next time you open the same recording, including in later sessions. The same value is used by the audio player, so playback loudness and displayed levels stay consistent.

Troubleshooting

Symptom or message	Cause and remedy
"No live signal. Start Preview (Online Monitor) first — pistonphone calibration reads live raw V RMS from the running stream."	No data is streaming. Start Preview in the Online Monitor, confirm the frontend is selected and the channel is enabled.
Capture stays disabled	No channel is selected, or the live RMS is zero. Check that the channel's On box is ticked and that the calibrator is switched on.
Apply stays disabled	Nothing has been captured yet, or the computed sensitivity is zero. Capture a valid reading first.
Live RMS reads zero or near zero	The calibrator is off or badly seated, the wrong channel is selected, or the sensor supply is wrong. Check that Supply is set to ICP for a CCLD microphone.
Live RMS is unstable	The calibrator is not seated squarely, or there is strong background noise or air movement. Reseat and wait longer before capturing.
Sensitivity is about ten times too large or too small	The wrong reference level is selected. Switch between 94 dB and 114 dB — the result recomputes without re-capturing.
Sensitivity far from the data-sheet value	Check the input Range (a clipped signal reads low) and the Highpass setting, and confirm you calibrated the channel the microphone is actually plugged into.
Levels wrong after re-cabling	The calibration belongs to a specific chain. Re-calibrate after any change to cable, channel, range or supply.
Analysis levels differ from live levels	Check the playback SPL Calib: fields for that file — they are stored per file and may carry a value from an earlier session.