M. ZEN 3-Channel X-LMS Controller User Manual Version 3.1 Written by: Alex Boudreau, Ph.D.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. TABLE OF CONTENTS 1.0 Introduction................................................................................................................... 3 2.0 Software Installation ..................................................................................................... 7 3.0 Detailed Control Algorithm .......................................................................................... 9 3.1 Uncoupled Algorithm Description.....
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 1.0 Introduction The ZEN controller presented in this document is based on the Signal Ranger Mk2 DSP board and the SR2_Analog8 expansion board from Soft dB. The Signal Ranger Mk2 DSP (Digital Signal Processor) board has the following features: 1) 2) 3) 4) DSP (TMS320C5502@300 MHz) 16-bit fixed point from TI. FPGA (XS3S400) with 63 user-programmable digital I/Os from XILINX. High speed USB 2.0 interface.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Figure 2: SR2_Analog_8 (or 16) expansion board The features of the SR2_Analog_8 expansion board are: 1) Four stereo 16-bit ADC/DAC converters from TI providing eight analog I/Os. 2) A main sampling frequency of 78 kHz. The optimization rate can be adjusted using a decimation factor. 3) Signal on noise ratio: 88 dB (input) and 90 dB (output). 4) Adjustable input gain, from 0 to 54 dB. 5) Direct or microphone input for Electret microphones.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. The two ZEN controller boards are housed in a metal enclosure: Figure 3: Metal enclosure of the ZEN controller Figure 4 shows a schematic of the ZEN active control system. In addition to the DSP board, the system includes a PC (with a dedicated user interface) to control the DSP board over a USB link. The controller provides six inputs (three for the reference signals and three others for the error signals).
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Figure 4: Schematic of the ZEN 3-channel control system from Soft dB The real-time algorithm running on the DSP board synthesizes the output signals to minimize the noise measured by the three error sensors. The X-LMS algorithm with feedforward and a filtered reference LMS optimization is used to minimize the error signals.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 2.0 Software Installation To install the ZEN controller software, click on Setup.exe on the installation CD. The following files will be transferred to the PC: File name ZEN_Ver3_x.exe Folder C:\Program Files\ZEN_SoftdB SRanger2.dll C:\Program Files\ZEN_SoftdB default.cfg C:\Program Files\ZEN_SoftdB mainsetup.cfg C:\Program Files\ZEN_SoftdB CodeControl_SR2.out C:\Program Files\ZEN_SoftdB codeiden_sr2.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. The most important files are: 1) ZEN_Ver3_x.exe: the PC user interface of the ZEN controller 2) ZEN_UserManual.pdf: the ZEN user manual. Once the software is installed, the DSP board can be connected to the PC. At first connection, Windows asks for the USB driver. During USB installation, the user must manually specify the following folder: C:\Program Files\ZEN_SoftdB\DriverUSB. ZEN User Manual p.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.0 Detailed Control Algorithm The control algorithm running on the DSP board is an X-LMS feed-forward algorithm with filtered reference. The X-LMS optimization is done in real time for an optimization frequency that is selectable between 78.125 Hz and 78.125 kHz. The main sampling frequency is fixed at 78.125 kHz and the user can adjust the optimization rate by specifying a decimation factor.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Figure 5: Schematic for the uncoupled version of the control algorithm The table below describes the nomenclature of each signal and function illustrated in Figure 5: Signal or function Rx(n) Cx(n) Ex(n) Mu F_Rx F_Ex F_Cx CxEy CxRx Wx Norm x LMS_x W.N. Description Note: x and y are the output / input numbers Reference signal x. These signals are filtered by an adjustable high-pass filter to remove the DC component of the signal.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. schematic shows three generators but only one generator is used for all references. The reference signals are filtered by an adjustable band-pass filter (F_Rx) (see section 4.1). Next, the contribution of the control output signals is subtracted from the reference signals. The primary control path filters (CxRx) are used to predict the contribution of the control outputs on the reference signals (see section 3.1.2).
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.1.2 Subtracting the control output contributions from the reference signals As illustrated in Figure 5, the control algorithm includes the evaluation and the subtraction of the control output contributions from the reference signals. Even with great precautions during the mechanical design of the control system, noise generated by control sources can add perturbation noise to the reference signals.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Figure 8 : Autospectrum of a reference signal (control ON and subtraction OFF) To be able to make an adequate subtraction of the control output contributions, the primary path control filters must be identified (filters CxRx). To reduce calculation time, only the direct primary control path filters are used.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.1.3 Adding low-level white noise to reference signals The ZEN controller allows the addition of a low-amplitude white noise to reference signals. This white noise is useful for preventing saturation of the control filter coefficients when the system to be controlled is ill-conditioned. If the error surface has very flat axes, the X-LMS algorithm can make changes to the control filter coefficients following these axes without constraint.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.1.4 Adaptative step size normalization technique Normalization of the adaptative step size allows an optimal convergence rate of the LMS algorithm.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.2 Description of the control algorithm for the coupled case Figure 9 shows a schematic of the coupled version of the controller. Unlike Figure 5 which shows the uncoupled version, the secondary cross-paths CxEy (x≠y) are now included. This implies three optimizations for each channel using all error signals. This algorithm requires three times the computation time of the uncoupled version.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.3 Description of the control path identification algorithm Note: This identification technique is based on the hypothesis that the primary noise source to be controlled, is off during the whole identification process. However, an identification technique for noisy conditions is provided later in this section. 3.3.1 Identification algorithm implemented on the DSP The control paths must be identified before launching the control.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. The F_Ex, F_Rx and the F_Cx (if used) filters are activated during the identification phase. This way, the identified CxEy and CxRx filters include the band-pass filter and can be used directly during the control phase. The comparison of the energy of the secondary cross-path filter (CxEy) with the direct secondary control path filter (CxEx) can help to select coupled or uncoupled mode.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 3.3.2 Adaptative step size and identification technique in noisy conditions The normalization of the adaptative step size of the identification module is done at high level on the PC based on the number of coefficients used and the amplitude of the white noise. In theory, if the primary noise to be controlled is not activated, the use of Mu=1 obtains the fastest convergence rate and great precision of the identified model.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 4.0 User interface The next sections provide a detailed description of the PC user interface developed for the ZEN controller. Each section can be used individually for reference purposes. However, section 4.0 and the other sub-sections are written as a procedure. Figure 11 and Figure 12 show two clips of the main interface of the ZEN controller. This interface has four tabs.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Figure 12: PC user interface of the ZEN controller (main tab) The next figure presents the last tab. This tab is used to manage the autonomous mode. The functions of this tab are offered as an option (contact Soft dB for price and availability). ZEN User Manual p.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 4.1 Configuration interface of the controller Before launching the identification of the control path filters and the control, the user must set the controller parameters. At interface start-up, only the Set-up general and Open CFG functions on the main tab are accessible (see Figure 12).
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. General Parameters These parameters allow selecting the controller mode (coupled or uncoupled), the number of channels and the sampling frequency (through the decimation factor). The main sampling frequency must be set to 78.125 kHz to help minimize loop-back delay. Next, the decimation factor can be used to adjust the optimization rate (or the decimated sampling frequency).
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. The main function of the band-pass filter is to force the control to work only on a selected frequency band. The band-pass filter also acts like an anti-aliasing filter: high-frequency sampling (78.125 kHz) along with the decimation technique, allows a very short group delay but the aliasing can be a problem without the addition of a numerical anti-aliasing filter.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Secondary control path parameters (filters CxEy) The parameters for the secondary path filters are: the number of coefficients of the CxEy filters, the adaptive step size of the identification LMS and amplitude of the white noise used during the identification process. The CxEy filters are used during the control phase to filter the reference signals before X-LMS optimization.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. impulse response. A longer DC filter impulse response implies longer CxRx, CxEx and control filter response. A frequency cut-off of between 30 Hz and 50 Hz is adequate. Use Bandpass filter on outputs By default this option is set to Yes. When the band pass filter is used on the outputs, the aliasing is avoided on the control signals. However, the delay associated with the bandpass filter implies a larger loopback delay.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 4.2 Control path identification interface The second step after setting-up of the controller (see section 4.1) is identification of the control paths. Primary control path identification must be done first (control Primary path identification). The main interface does not allow identification of the secondary control path (control Secondary path identification) as long as primary control path identification has not been done.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. During the identification process, the user should pay special attention to be sure that the number of coefficients used is adequate. This means that the energy at the end of the FIR impulse response should be low (select the time tab on the upper graph of Figure 15). If required, the number of coefficients can be increased in the configuration dialog box (function Set-up General in the main interface).
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 4.3 Control interface Before launching the control, we suggest the configuration and identification results be saved. The SaveCFG and OpenCFG functions on the main interface allow the user to save and recall all configuration parameters and identification results. So, it’s always possible to recall an old configuration and to launch the control.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. An estimate of the attenuation (or noise reduction) is presented in the upper right corner. Overall attenuation can be displayed for all channels (an average is done) or for a selected channel following the state of the control Att. type and Show filter Wx. The following equation is used to provide an instantaneous estimate of the attenuation: 2 256 ∑ Error Att.inst.=10⋅Log10 2561 2 ∑Re f.
User manual for the ZEN 3-channel X-LMS controller OutCxEy Mux_Ex Rx_clean Soft dB inc. The filtered reference at the input of the X-LMS The error signals multiplied by the normalized adaptative step size. Note: the Mux_Ey are not accessible. Reference signals with the subtraction of control source contribution Note: All signals are in I16 format (16-bit signed integer) and can vary between 32768 and 32767.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. Another function not yet presented is See info. Figure 17 shows the dialog box for this function. The dialog box includes many tabs, providing access to the whole configuration, identification results and current control filters. Figure 17: Information dialog box (Secondary Path CxEy tab) The CxRx, CxEy and Wx filters can be observed and saved using the Export Graphs control.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. 4.4 Autonomous mode (optional) The autonomous mode is optional. Ask Soft dB for pricing and availability. This mode can be used to allow obtaining a stand-alone control system. When the control system is configured and operational, the entire configuration can be downloaded in flash memory of the ZEN. Then, the control phase is automatically launched when the ZEN is powered up.
User manual for the ZEN 3-channel X-LMS controller Soft dB inc. detected on the error signals. The next figure shows the PC interface when the autonomous test is running: Figure 19 : Autonomous Mode Tab (Test Autonomous Mode) During the autonomous mode, the processor in the ZEN unit observes the error signals and if saturation is detected, the normalized MU is divided by 2 and the control filters are reset. After multiple saturations, the normalized MU reaches zero and the controller is stopped.
