Mµ64 Control
Like all control pages, the Mµ64 page provides real-time monitoring of device operation. This is not a measurement interface. The displays are informational (RMS activity, time signal, spectrum, octave bands, etc.) and are intended to verify the proper operation of all microphones for different acquisition parameter values.
However, control pages do allow real-time signal recording, according to the selected parameter configuration.
The Mµ64 control page is divided into two sections: the horizontal control menu bar at the top of the window, and the displays below.
Menu bar
The menu bar has three sections:
- acquisition control buttons
- a status window displaying current parameter and activity states
- Mµ64 controller configuration buttons
Acquisition controls
Without changing anything else, you can already start an acquisition and recording using only these buttons.
- Select sampling rate
- Select acquisition duration (0 means unlimited duration)
- Full Mµ64 controller reset (use only in case of issues)
- Start acquisition
- Start recording
Start an acquisition
You can start an acquisition only if an Mµ64 controller is connected to your computer via USB.
On macOS, as on Windows, you must install the USB driver beforehand (see documentation).
If these two conditions are met, you should see the green Mµ64 controller presence icon at the top of the page, in the icon bar.
Also, the acquisition start button (4) must be active (clickable, green).
Click the acquisition start button (4). It turns into a stop-acquisition button while the counter starts running in the status bar. The MEMS RMS activity display should become active, depending on ambient acoustic activity.
Click the stop-acquisition button again. The counter stops, and acquisition ends.
During acquisition, the red acquisition LED on the Mµ64 unit should light up. This indicator confirms that acquisition is actually running at hardware level.
Record
To record an ongoing acquisition, click the record button. It turns red, meaning data recording is in progress. Click it again to stop recording.
Recording is independent from acquisition. If you click BEFORE an acquisition, recording will only start when acquisition starts. If you stop recording DURING an acquisition, the acquisition continues after recording effectively stops. If you stop acquisition DURING recording, recording stops automatically.
Recorded signals are always the raw signals from the concentrator (24-bit encoded on 32-bit integers), regardless of processing performed on the control page.
Configure acquisition
The three buttons below let you modify acquisition and recording parameters. These parameters cannot be changed during acquisition. The buttons become non-clickable:
- Recording parameters
- MEMS and analog channels activation for recording
- Acquisition parameters
Recording parameters let you define the destination folder and recording file names. If you do not change them, default values are used.
By default, recording files are never overwritten. If you perform several recordings in a row without changing the file name, the current name is reused and automatically numbered to prevent overwriting.
The MEMS and analog channel activation button opens a channel selector that lets you choose which channels to record.
By default, all MEMS are selected, as well as the counter channel, but not analog or status channels. You can change this selection as needed.
The status channel cannot be selected in MµBoard versions up to and including 4.1.20.
In those same versions, the counter channel is mandatory because it is used to verify data integrity.
Only selected channels are recorded during recording sequences. Note that activity from non-selected MEMS is not transmitted by the concentrator. These channels can therefore no longer be processed by the software.
You can close the window and discard your changes using the "CANCEL" button or by pressing ESCAPE on your keyboard.
Below, the configuration button opens a form that lets you adjust acquisition settings:
On the left side, it includes sensitive settings, some of which should not be modified:
- Number of USB transfer buffers (default: 8)
- Buffer size in number of samples (default: 1024)
- Reference sampling rate
- Spectrogram cutoff frequency
- Synchronization delay
The number of "circular" buffers determines real-time USB transmission quality. There must always be at least two buffers to ensure lossless transmission. The higher this number, the safer lossless transmission is, at the cost of potentially increased latency. The default value is 8, which is fully sufficient for standard use (assuming the same USB bus is not heavily used by another bandwidth-hungry device).
Buffer size is up to the user. However, it affects how the control page processes signals. Energy and spectrum calculations are performed exclusively over these window widths. That is why the corresponding time duration (depending on sampling rate) is also displayed.
The reference sampling rate must not be changed. By default, it is set to the frequency programmed on the FPGA. Our systems can be configured with either a 50 kHz or 48 kHz reference frequency.
If you use 48 kHz as the reference while the concentrator FPGA is programmed at 50 kHz, all values estimated by the software will be off proportionally.
The spectrogram cutoff frequency limits spectrum display to frequencies below that value. This can be seen as a low-frequency zoom and has no impact on recorded signals.
Synchronization delay should remain at its default value (10 for medium to large microphone arrays). For very small arrays (very short cables), this value should be reduced; conversely, it should be increased for very large arrays. An estimator for the optimal value of this parameter will be included in a future version of MµBoard.
Status window
The status window displays the values of the main acquisition parameters:
- Sampling rate: current sampling rate
- Clockdiv: concentrator internal clock division factor. It allows derivation of the exact sampling rate (see below)
- Frame counter: frame counter
- Update frequency: data refresh rate on screen
- Frame lost: number of lost frames during acquisition or since the beginning of the last acquisition
- Timer: elapsed time in minutes and seconds since acquisition started
- Activated MEMS: number of activated MEMS
- Activated analogs: number of activated analog channels
- Counter: counter activation state
- Status: status line activation state
- Buffers duration: buffer duration in milliseconds
- Buffers number: number of buffers allocated for transfer
- TotalRMS: average power in dB over all active microphones (excluding analog channels)
- Timer: elapsed time since acquisition start, in minutes and seconds
Displays
The second part of the page, below the control bar, displays a set of real-time indicators computed from signals coming from the concentrator.
RMS levels and selection
This window displays real-time RMS levels in dB for all MEMS. The magnitude slider on the right adjusts the color visualization scale for power levels. This slider also affects the spectrogram display. Its lower and upper defaults are 30 dB and 90 dB.
If you want a quick visual check of all MEMS operation, set the lower slider to 0 dB. All active MEMS should then show activity. Otherwise, inactive MEMS may belong to an array not connected to the concentrator, may have been deactivated, or may be defective.
The tiles in the checkerboard representing MEMS activity are clickable. If you click one tile, the selected MEMS number is shown in other window headers and in the status bar (Selected Channel (SC)). This means the displayed activity in those windows corresponds to the selected MEMS. By default, the selected MEMS is MEMS 0 (first microphone of the first array).
Octave spectrum
This window shows octave-band frequency analysis of the selected MEMS.
Signal
Activity of the selected MEMS. In this version of MµBoard, not all samples are displayed. For each received frame, only the minimum and maximum values of the measured frame signal are shown.
Spectrogram
This window displays the spectrum computed from frames as they arrive. As noted above, acquisition frame size is used as the FFT calculation window. The spectrum is shown from the first frequency to the last (Fe/2).
The displayed frequency range can be changed in settings (see the settings button in the control bar above).
Spectral correction
This is the correction curve applied to the spectrogram before display. MEMS frequency response is approximately flat between 100 Hz and 10 kHz, but this is no longer true between 10 kHz and 20 kHz. This curve, measured in the lab on 1024 MEMS, provides the average correction needed to recover an approximately flat response up to 20 kHz. This correction is applied by default. You can disable it by clicking the button on the right side of the window title. The graph then changes from green to gray.
Spectral correction is not applied to recorded signals, only to the displayed spectrogram.