Focus Fidelity. Impala. Impulse Response Measurement. User Manual

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Focus Fidelity

Impala

Impulse Response Measurement

User Manual

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Contact & Support

For technical support and other enquiries please use the contact form on our website or the e-mail address below.

e-mail: [email protected] web: www.focusfidelity.com

Software Activation Requirements

Focus Fidelity’s impulse response measurement application is distributed free of charge, but activation of the application does require that the end user’s e-mail address be subscribed to the Focus Fidelity mailing list.

Sign up to the mailing list can be completed at https://www.focusfidelity.com/

E-mails are sent out to subscribers infrequently and typically contain updates on product development and software releases.

The sign-up form may not work correctly and appear unresponsive if your web browser has security settings set to strict. Lowering the security setting might be required.

System Requirements

Operating System: Microsoft Windows 10 or 11 Memory: 8GB

CPU: Intel or AMD x64 with AVX instruction set support.

Disk Space: 200MB

Required Hardware

The measurement application will play a frequency swept sine-wave through your loudspeakers and record the result with a measurement microphone.

This requires a USB DAC or similar audio interface to be connected to your PC along with a suitable measurement microphone.

Typically the DAC or other interface already used for music playback combined with a USB measurement microphone is all that is required.

Examples of USB measurement microphones include

https://www.minidsp.com/products/acoustic-measurement/umik-1 https://www.minidsp.com/products/acoustic-measurement/umik-2

https://www.daytonaudio.com/product/1116/umm-6-usb-measurement-microphone https://cross-spectrum.com/measurement/calibrated_umik.html

Alternatively, a microphone with an analogue signal output can be used in conjunction with an audio interface which includes a microphone pream- plifier and analogue to digital converter.

Examples of analogue microphones include,

https://www.daytonaudio.com/product/911/emm-6-electret-measurement-microphone https://earthworksaudio.com/measurement-microphones/m23/

https://www.cross-spectrum.com/measurement/calibrated_dayton.html https://europe.beyerdynamic.com/mm-1.html

An audio interface with a suitable microphone input will most likely also have a built-in digital to analogue converter and analogue outputs for con- nection to your amplifier. For example,

https://motu.com/en-us/products/m-series/m4/

A proper microphone stand is also highly recommended, for example,

http://www.samsontech.com/samson/products/accessories/microphone-stands/mk10/

USB cables of adequate length are also a must-have, the USB 2.0 specification allows for cable lengths up to 5 meters. Longer cable lengths require an active extension cable. For example https://www.startech.com/en-nz/cables/usb2aaext10m

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Introduction

Focus Fidelity's impulse response measurement application, Impala, is available for download free of charge. This application has everything you need and nothing you don't for taking measurements for digital room correction.

Key features include,

Measurements of left and right channels taken at multiple positions are saved to a single file (*.ffm) to be opened in Focus Fidelity's filter design software.

Measurements may also be exported as *.wav files for use with 3rd party software.

Exported measurements have the microphone calibration applied.

The relative timing of the left and right channels is captured.

The *.ffm file includes microphone calibration and relative timing information, creating a seamless workflow with Focus Fidelity's filter design software.

Audio hardware is accessed via the Microsoft Windows WASAPI exclusive mode interface eliminating issues with Windows audio mixers and sample rate converters.

Measurements can be taken with a correction filter applied. The filter is applied to the test signal the same way it is to music which allows the performance of the filters to be verified.

Tested with MiniDSP UMIK-1 & UMIK-2 microphones and XMOS based USB Audio interfaces.

A pink noise generator and sound pressure level meter is included for setting the volume level.

Future features will include, Waterfall & spectrogram plots.

Additional channels when required for digital crossovers, including subwoofer integration.

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Windows Audio Device Configuration

Audio interfaces are accessed via the Microsoft Windows WASAPI interface in exclusive mode. It is necessary to ensure that exclusive mode is enabled for the audio devices you wish to use.

Open the sound settings,

Click Sound Control Panel in the Related Settings section.

On the Playback tab. Select your audio interface and right click,

Select Properties,

On the advanced tab ensure that both check boxes in the exclusive mode section are checked.

Click OK to close the Speaker Properties dialogue.

Select the Recording tab in the Sound dialogue, select your microphone and ensure the same exclusive mode settings are checked.

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Microphone Level Setting

To ensure the correct operation of the SPL meter feature of the software and prevent clipping due to excess digital gain, the microphone level settings must be set to a gain of 0.0dB.

Open the sound settings,

Click Sound Control Panel in the Related Settings section.

On the Recording tab. Select your microphone and right click,

Click Properties.

Click on the Levels tab. Right click on the number to the right hand side of the slider. Select decibels from the menu.

Use the slider control to adjust the level to 0.0dB.

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MiniDSP UMIK-2 Level Setting

If you are using a MiniDSP UMIK-2 microphone ensure that the level settings are turned all the way up in the MiniDSP UAC2 Control Panel.

The control panel is opened from the windows system tray,

Select the volume tab on the control panel, click the Input button,

Ensure that the input volume slider controls are turned up all the way.

This should correspond to 0.0dB in the Microsoft Windows device properties.

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Software License Activation

Starting the application for the first time will automatically show the license manager dialogue,

Enter the e-mail address you used to subscribe to the Focus Fidelity mailing list and click Check E-mail.

The dialogue will show Activation Complete.

Close the License Manager dialogue.

If you get an error message showing UnknownNetworkError then your PC is likely missing some required libraries. Please see the troubleshooting section at the end of this manual.

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User Interface Overview

The graphical user interface includes a toolbar at the top of the window for quick access to all features. All the buttons include hover help text.

The status of the audio stream is shown at the bottom right of the window.

Toolbar

Create a new Focus Fidelity measurement project.

Open an existing Focus Fidelity measurement project file (*.ffm).

Save the currently open project.

Save the currently open project to a new file.

Close the currently open project.

Open the project setup dialogue.

Open the audio hardware setup dialogue to select audio input and output devices.

Open the microphone calibration setup dialogue.

Open the pink noise generator dialogue.

Export measurements to *.wav files.

This is not required in the Focus Fidelity workflow (the Focus Fidelity measurement project is opened directly in the filter design application).

Open the user manual pdf document (requires a pdf file viewer installed).

Open the check for updates dialogue.

Open the license manager dialogue.

Open the product and license information dialogue.

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Graphs

The user interface employs graphs to display time and frequency data. Some of the features of and essential interaction with these graph displays are described here.

The graph area for each graph is the box defined by the X and Y axes. Holding down the left mouse button in the graph area will bring up a legend with the names and values of each of the traces on the graph. Dragging the mouse with the left button held down will update the values correspond- ing to the cursor position.

Zooming in on the graph is accomplished by holding down the right mouse button and dragging a rectangle over the desired area. Releasing the right mouse button will zoom in.

Zooming out is accomplished by double clicking the right mouse button.

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Project Creation & Setup

This section describes how to create & configure a project, select the audio interfaces and setup the microphone calibration.

Creating a Project

Click the new project button to create a new measurement project.

This will open the project setup dialogue,

Project Name

Enter a suitable name or description for the project.

Number Of Measurement Positions

Select the number of measurement positions. This is the number of microphone positions at which measurements will be taken. Six to 10 positions work well. More advice on microphone positioning is provided later in this document.

Measurement Sample Rate

Select the project sample rate. This is the sample rate at which measurements will be taken.

Some notes on sample rate selection,

The sample rate selected must be supported by the audio interfaces connected to the PC.

48000 S/s is the recommended rate and is the only rate supported by some USB measurement microphones.

Sample rates higher than 48000 S/s are not required and will significantly increase the length of time needed to generate room correction filters.

Focus Fidelity’s filter design software will generate filters for all typical sample rates regardless of the sample rate used to perform the measurements.

Measurement Length

This is the length of the frequency swept sine test signal and the resulting impulse response.

Set this to the longest option.

Test Signal Infrasound Content

Setting this option to Reduced lowers the signal strength of the frequency swept sine wave below 20Hz. The reduction is approximately 15dB.

Select Reduced for measuring smaller loudspeakers which will not reproduce and may be overloaded by low-frequency content.

Select Standard for larger loudspeakers and subwoofers, which will operate to 20Hz or below.

Filter

A previously generated room correction filter may be loaded here. The filter is applied to the frequency swept sine test signal as it would be to mu-

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sic. The measurement project would then be used to verify the performance of the filter.

The filter must have the same sample rate as the project.

The filter option must be skipped to take measurements that will be used to generate a room correction filter.

Changing the Project Setup

To edit the project setup after creating the project, click the project setup button.

Once the first measurement has been taken, it will no longer be possible to change the project settings.

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Audio Hardware Setup

To select audio input and output interfaces click the audio hardware setup button.

The Audio IO Setup dialogue will open,

Input & Output Device

Select the audio input and output interfaces from the drop-down menus.

The application detects audio devices available on the Microsoft Windows WASAPI interface.

The audio devices you wish to use must have exclusive mode enabled. They will not appear in the list if exclusive mode is disabled.

Automatically set the input device gain to 0.0dB

To ensure the correct operation of the SPL meter feature of the software and prevent clipping due to excess digital gain, the microphone level settings must be set to a gain of 0.0dB.

When this check box is selected, the software will automatically set the input device level controls to a gain of 0.0dB. The gain is set when the audio stream starts.

Note that when using the MiniDSP UMIK-2, it is still necessary to check the Input Volume levels in the MiniDSP UAC2 Control Panel as previously described in this manual.

Buffer Size

This setting is the number of audio samples transferred between the application and the hardware in one transaction.

The lowest setting, approximately 20 milliseconds, should work reliably on most PCs.

Slower PCs may require a larger setting.

The application will alert the user with error messages if there is an issue with the audio streaming.

Microphone

The audio interface which the microphone is connected to may have multiple inputs, use this setting to select which input channel the microphone is connected to.

For USB measurement microphones select Device Input 0.

Left Speaker & Right Speaker

The audio interface which the loudspeakers are connected to may have more than two output channels, use this setting to select which output channel the left and right speakers are connected to.

For two channel stereo interfaces such as a USB DAC the left speaker should be Device Output 0 and the right speaker should be Device Output 1.

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Microphone Calibration

Click the microphone calibration button on the toolbar to open the calibration dialogue box.

Click Import File and select your calibration file. Which calibration file to use, 0 degrees or 90 degrees, is discussed in the Microphone Posi- tioning section later in this manual.

The software supports the most common formats and imports the magnitude frequency response data, which is displayed on the graph.

The microphone calibration file may include the microphone’s sensitivity. It would typically be the first line in the file. For example, Sensitivity 4.758 dBFS or "Sens Factor =4.758dB, AGain =18dB, SERNO: 7076138"

The software will load the sensitivity value and display it in the Microphone Sensitivity box. The sensitivity value can be manually entered if required.

Importing the microphone’s sensitivity is not required for performing measurements. However, it is required for the correct operation of the sound pressure level meter feature, which is used to set the audio volume as described in the next section.

Click OK to close the dialogue box.

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Setting The Volume Level

A pink noise generator is included in the software to aid in setting the volume level to be used for performing measurements.

Ensure that the microphone gain is set to 0.0dB as previously described in the Microphone Level Setting section of this manual.

Click the pink noise generator button in the toolbar.

The sound level check window will open,

Turn the volume control on your amplifier all the way down.

Select the output channel using the drop down box located at the bottom left of the window.

Click Start Audio. Slowly increase your amplifier’s volume control.

If your microphone calibration data includes a sensitivity value then the sound pressure level will be displayed.

A sensible sound pressure level for performing measurements is about 70dB.

Please note that the sound pressure level displayed relies on the sensitivity data of your microphone being correct.

Do not turn the volume up to a level higher than what you are comfortable with.

The volume control setting arrived at here should be used for performing measurements as described in the next section.

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Performing Measurements

This section describes how to position your measurement microphone, followed by the operation of the software.

Microphone Positioning

The first measurement you will perform is at the main listening position. This position is the “sweet spot” of the listening area where you would typically sit for critical listening. The microphone should be at the height your ears would be.

The software will use the measurement taken at the main listening position to time-align the left and right channels.

There are two common microphone orientations used for room correction measurements. The first is horizontal and pointing halfway between the left and right speakers. In this case, you should use the 0 degrees microphone calibration file. The second orientation is to point the microphone at the ceiling. In this case, use the 90 degrees microphone calibration file.

Focus Fidelity recommends that you use the horizontal orientation.

You should arrange the remaining positions symmetrically around the main listening position with variations in height.

The measurement positions should cover the intended listening area, for example, the width of a sofa.

You can use a tighter spacing between the measurement positions for a single-seat listening arrangement.

There is no exact science to positioning the microphone; however, a total of 8 to 10 measurements will provide enough data.

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Software Operation

With the new project created and configured, your screen should now appear like this,

This project has been created with eight measurement positions. There is a row in the table for each measurement position.

Ensure that there is no background noise.

Ensure that the volume on your amplifier has been appropriately set as previously described The volume must not be changed once the first measurement has been taken.

All measurements must be taken at the same volume setting.

The microphone signal graph shows the signal level as a percentage of the maximum level. A signal level of 100% is the signal clipping. The software will display an error and discard the measurement if signal clipping is detected.

Clicking the play button in the Main Listening Position row will play a frequency swept sine signal through the left speaker followed by the right speaker. The recording will be processed and stored in the Main Listening Position row.

Move the microphone to the next measurement position and click the play button in the next row. Repeat for all remaining measurement positions.

Save the project; it is saved as a *.ffm file which you can open in Focus Fidelity’s Filter Design software.

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License Information

End User License Agreement

A copy of the End User License Agreement is provided with the software and is located here License_Docs\EULA.rtf

which is located in the software installation directory typically, C:\Program Files\Focus Fidelity\FFM\License_Docs\EULA.rtf

Licensed Components

Focus Fidelity software uses the Qt ( https://www.qt.io/ ) cross platform user interface and application framework, it is licensed under the GNU Les- ser General Public License (LGPL) v3 license ( https://doc.qt.io/qt-5/lgpl.html ).

Copies of relevant licenses for Qt and other components are distributed with this software, these are stored in the License_Docs\Licensed_Components\

directory which is located in the software installation directory typically,

C:\Program Files\Focus Fidelity\Focus Filter Designer\License_Docs\Licensed_Components\

About Dialogue

The about dialogue can be viewed by selecting About from the Tools menu. This provides software version information and a list of licensed components.

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Installation Troubleshooting

**Missing *.dll File Error Messages On Program Start**

If running Impala results in missing *.dll file error messages such as MSVCP140.dll or VCOMP140.dll etc. then your PC does not have the required Microsoft libraries installed. To install these files go to the Impala installation folder and run vc_redist.x64.exe

Unknown Network Error

If activating your license or checking for updates results in an UnknownNetworkError then it is likely that your PC does not have the Microsoft Visual C++ 2010 x64 redistributable installed.

To install these libraries go to https://www.microsoft.com/en-nz/download/details.aspx?id=26999 and download and run vcredist_x64.exe

Program Does Not Start

The program requires that the CPU in your PC support the AVX instruction set, if it does not the program will fail to start and will not display any error messages. To determine if your CPU includes the AVX instruction set go to https://www.cpuid.com/softwares/cpu-z.html and download and install CPU-Z. Run CPU-Z,

The list of supported instructions is shown at the bottom of the processor section.

AVX instructions were introduced in 2011, only very old or low power CPUs will not include the AVX instruction set.

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Revisions

Revision Date Description

1.0 14/11/2021 Initial Issue

1.1 16/12/2021 Updated system requirements. Added microphone level setting.

1.2 17/12/2021 Added UMIK-2 level setting instructions.

1.3 19/12/2021 Added notes on microphone signal level and signal clipping detection.

1.4 23/12/2021 Added automatic gain setting on input device.

1.5 03/01/2022 Added notes on microphone calibration file selection. Added Installation Troubleshooting section.

1.6 08/01/2022 Updated troubleshooting section.

1.7 09/01/2022 Added Reduced Test Signal Infrasound Content option in project creation section.

1.8 15/01/2022 Updated microphone calibration section.