Using ADM in depth
Audio setup, calibration, engine settings, reading the plots, the curve library and exports.
Audio setup
ADM plays the sweep and records the result at the same time, so it needs an audio device with both an output and an input. The Audio Setup window lets you choose the driver, the device, the sample rate and the buffer size. On Windows, ADM supports ASIO and WASAPI. The status bar shows the sample rate, bit depth, buffer size and sweep duration currently in use.
Connect the output of the interface to the input of the device under test, and the output of the device under test back to an input of the interface.
Calibration
Two calibrations make the readings accurate:
- Latency calibration measures the delay of your audio system in samples and milliseconds, so the response can be aligned correctly in time.
- Amplitude calibration normalizes the linear response so that its level reads 0 dB, using the mean level over the sweep’s frequency range. After that, the harmonic curves are read relative to the linear response.
Engine settings
The Engine Settings window groups every parameter of the measurement. Nothing about the excitation is fixed.
| Group | What you can set |
|---|---|
| Method | Farina ESS (exponential) or Novák SSS (synchronized). With Novák, the sweep duration is adjusted automatically so the phases stay synchronized. |
| Frequency range | Start and end frequency (default 20 Hz to 20 kHz). |
| Level | Level of the sweep in dBFS (default −3 dBFS). |
| Duration | Sweep time (default 0.5 s), plus silence before and after the sweep. |
| Fades | Fade-in (default 50 ms), fade-out (default 10 ms) and the shape of the fade (cosine or linear). |
| Extraction windows | The short fades applied at the edges of each harmonic window (default 5 ms). |
Buttons let you restore the defaults, generate and play the sweep to preview it, and save the settings. ADM builds the sweep from your saved settings when it starts. After you change parameters, press Save to make the new sweep the active one for the next capture. A status log reports what ADM is doing, and invalid combinations of parameters are highlighted as you type.
For the reasoning behind these parameters, see the method behind ADM.
Running a measurement
Press Start Capture. ADM plays the sweep in a loop and refreshes the plots after every pass; the button reads Running while it works. Now change the device itself (turn a gain knob, swap a component, switch a mode) and watch the curves follow. Press the button again to stop.
Engine Settings and the calibrations are locked while a capture is running, so change them between captures.
Reading the plots
Frequency plot. Shows the magnitude in dB against a logarithmic frequency axis, from 20 Hz to 20 kHz. It can draw the linear response and up to five more curves for the higher orders, each with its own colour. The Order control chooses how many orders are shown. Curves from the library are drawn on top in the same colours, with a dashed line style.
Time plot. Shows the full deconvolved response, with the extraction window of each order drawn on top for the live measurement. This is the place to check that the windows sit where you expect, especially with very short sweeps, where neighbouring windows get close to each other.
THD overlay. Turned on with the THD button, it applies to the live measurement. It marks the points where the harmonics of a 1 kHz tone fall (1 to 6 kHz), for the orders currently shown with Order (the 6 kHz point is the residual for orders above the fifth), with their levels in dB, and shows the resulting THD as a percentage.
You can zoom both plots. The Plots button cycles between both plots, the frequency plot only and the time plot only.
Curve library
Press Take New to store the latest measurement in the library, then tick a curve to show it on the plots. The library is a set of folders and curves that you can organize freely: create folders, rename, delete (items go to the Recycle Bin), drag and drop, and select several items with Ctrl or Shift. Each curve can be shown or hidden, and visible curves keep a distinct dash style, so several measurements can be compared on the same plot.
By default the library lives in Documents/ADM/Curves. You can open it in Explorer or change its location from the context menu.
Exporting
Saving a curve or a folder can produce:
- a copy of the
.admcurvefile, ADM’s own format, which keeps the full measurement and its settings; - a CSV file with the frequency in Hz and the level of each order in dB, on a grid of 1/48 octave;
- 32-bit float WAV files for the full deconvolved response and for each order’s impulse response.
Trademark
ASIO is a trademark and software of Steinberg Media Technologies GmbH.