Input Recording¶
Input Recording isn't tied to a specific calibration procedure. It's a general-purpose tool for capturing and reviewing whatever's coming into one or more input channels simultaneously.
Recording¶
Run CFTSCal and select the Input Recording workspace.
| Field | What it means |
|---|---|
| Number of inputs | How many channels to record at once, from 1 up to the total number your hardware exposes. |
| Input (one row per active channel) | A dropdown listing every available physical input — this doubles as the row's label, so there's no separate "Input 0"/"Input 1" text. Pick any channel here; the same physical channel can't be assigned to two active rows at once. |
| Sensor (per row) | A dropdown picking what kind of sensor is attached, plus (for most types) a second dropdown picking which specific one. |
| Gain (per row) | The preamp gain, in dB, currently applied to that row's channel. |
| Target folder | Organizes recordings into folders, same as every other workspace. Shared across all active channels, since they're saved together as a single recording. |
| Generator | A free-form label that can be used to record the details of the test stimulus. Click + to add a new one. |
Sensor types¶
| Type | What it means |
|---|---|
| Meas. Mic., Generic Mic., Input Amp., Starship | Loads a real, on-file calibration — pick the specific one from the second dropdown. This calibration converts the recorded voltage to Pascals. |
| Unity | A pass-through: records the raw voltage without converting it to Pascals. Since there's nothing to pick, the second dropdown is hidden. |
| Nominal | For a device with no measured calibration on file — e.g. going off a spec sheet value. Replaces the second dropdown with an mV/Pa field where you type the sensitivity directly; the recording is calibrated to Pascals using that value. Note the direction of the ratio: millivolts generated per Pascal, the convention used on most datasheets. If your datasheet gives Pa/V instead, take the reciprocal — see Which way round is "sensitivity"? |
Running the recording¶
To run the recording, click the Record button — this captures every active channel simultaneously, saved together as one recording. The button stays disabled until every active channel has a sensor selected and no two channels point at the same physical input; if that state is somehow reached anyway, clicking Record shows a warning explaining why rather than failing silently.
Reviewing the results¶
Select one or more recordings in the Recordings list to plot them. The Input Recording plot shows the calibrated time-domain waveform; the region you select drives both the PSD plot and the Analysis table below.
Recordings (the list) shows every recording ever made for this workspace, with the following columns:
| Column | Meaning |
|---|---|
| Name | Which folder the recording is filed under (usually the generator label). |
| Date | When the recording was made. |
| Generator | Which stimulus/generator label was used. |
| Channel | Which input channel(s) were recorded — comma-separated if more than one. |
| Sensor | Which sensor was attached to each channel — comma-separated in the same order as Channel. |
| Gain | The preamp gain, in dB, that was in effect for each channel — comma-separated in the same order as Channel. |
Each recording gets its own color, matching its highlight in the Recordings list. If a recording has more than one channel, all of its channels share that color but are distinguished from each other by line style (solid, dash, dot). The Analysis table groups its rows by recording for the same reason — each recording's channels appear as consecutive rows sharing one color swatch, with a Channel column distinguishing the rows within a group — alongside Duration, peak-equivalent SPL, and RMS dB SPL for whatever's inside the currently selected region.
Selecting a region¶
- Ctrl+drag anywhere on the time plot to draw a new region from scratch.
- Drag an edge of the existing region to resize it.
- Drag the middle of the region to move it without resizing.
- A plain drag (no Ctrl) pans the plot as usual.
Only the samples inside the selected region are used for the Analysis table and PSD.
Choosing a filter¶
The Filter dropdown controls the filtering that gets applied to the signal before it's plotted and the level is computed.
| Mode | What it does |
|---|---|
| Unfiltered | No filtering — deliberately not labeled "dBZ", since that would imply a standardized flat response over a defined range, and this is simply whatever bandwidth the raw recording happens to have. |
| dBA | Standard A-weighting (IEC 61672-1) |
| 1/3 Octave | A steep band-pass filter centered on a frequency you choose (Center freq.), with an adjustable order (higher orders roll off more sharply outside the band). |
Interpreting the levels¶
A single number describing a broadband signal's level always depends on how wide a band you're talking about, so it's worth knowing which quantity you're looking at:
- Spectrum level is the level in a 1 Hz-wide band — i.e. the level per hertz. This is what the PSD plot shows, at each frequency.
- Band level is the total level integrated over a band of width \(\Delta f\). This is what the Analysis table's RMS dB SPL reports, over whatever bandwidth the filter leaves in place.
They're related by:
Worked example. A flat noise with a spectrum level of 56 dB spanning 4–64 kHz has a band level of \(56 + 10 \times log_{10}(60000) = 103.8\) dB SPL. Note the \(10 \times log_{10}\) — this is a power ratio, unlike the \(20 \times log_{10}\) used for amplitude ratios elsewhere.
An unfiltered level often measures your noise floor
Because band level grows with bandwidth, a low noise floor spread across a wide bandwidth can dominate the reported total. For a 4 kHz-wide signal band at a 65 dB spectrum level (a 101 dB SPL band level) sitting on a flat noise floor that extends out to 50 kHz:
| Noise floor (spectrum level) | Reported total |
|---|---|
| 30 dB | 101.0 dB SPL |
| 40 dB | 101.2 dB SPL |
| 50 dB | 102.4 dB SPL |
| 60 dB | 107.7 dB SPL |
A noise floor 5 dB below the signal's spectrum level still adds 6.7 dB to the total, purely because it's 11 dB wider in bandwidth. This is why the region selection and the filter matter: restricting the analysis to the region and band you actually care about is what makes the reported level a measurement of your stimulus rather than of your noise floor. Total level is easy to get wrong has the full worked numbers.
Exporting a calibrated WAV¶
Right-click any recording (in Input Recording, or any other workspace's list) and choose Export as WAV… to save it as a standard WAV file, calibrated so that a sample value of 1.0 represents exactly 1.0 Pascal of sound pressure (with the exception of recordings generated by unity, in which case the output is 1.0 represents exactly 1.0 Volts). If the recording has multiple channels, they're exported as a single interleaved multi-channel WAV file, all channels sharing the same sample rate. The file also carries the recording's metadata (per-channel sensitivity, sensor ID, calibration date, etc.) embedded directly in it, in a way that doesn't interfere with normal playback.