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Focus Fidelity 'Filter Designer' and 'Impala': The Room Correction Software Package that Effectively Calibrates Audio Playback for Your Loudspeakers and Room Acoustics
Focus Fidelity 'Filter Designer' and 'Impala': The Room Correction Software Package that Effectively Calibrates Audio Playback for Your Loudspeakers and Room Acoustics
Focus Fidelity 'Filter Designer' and 'Impala': The Room Correction Software Package that Effectively Calibrates Audio Playback for Your Loudspeakers and Room Acoustics
The New Zealand-based audio software developer Focus Fidelity has recently released 'Filter Designer' (version 1.12.) and 'Impala' (version 1.14.) — The room correction software package that effectively calibrates audio playback for user’s loudspeakers and room acoustics resulting in higher fidelity. Filter Designer is the filter design application (available for $249 USD) and Impala is the measurement application (available for free). This software package generates the filters from measurements taken of the room and loudspeakers.
Focus Fidelity’s software uses multiple measurements taken at several positions in the listening area. The measurements combined with user-specified targets are the inputs to Focus Fidelity’s proprietary filter design process. As a result, users can expect accurate bass reproduction, improved stereo imaging, elimination of loudspeaker induced phase and impulse response distortions, and total control of tonal balance. Filter Designer generates filters compatible with audio playback softwares such as Accurate Sound's HLC, Roon, JRiver Media Center, and HQPlayer. These playback softwares with filter (convolution) capability are required to apply the filters to the audio signal.
Filter Designer analyzes impulse response measurements taken at multiple positions in the listening area to build a time-domain accurate mathematical model of the loudspeaker-input-to-listening-area “response” or transfer function. The model enables the identification of resonant modes, phase distortions, reverberant field tonal balance, and factors that should not be corrected. The input to the filter design process is the model analysis combined with the user-specified target magnitude frequency response.
Audio playback through the filter combines with the now known loudspeaker and room characteristics through measurements to produce a total result that is substantially closer to the frequency and time domain targets set by the user. The filter is particularly effective at reducing the decay time of resonances caused by standing waves (room modes)*, reversing loudspeaker phase and impulse distortions**, and controlling tonal balance.
The process of Filter Designer follows a “wizard” style left to right type workflow, beginning with importing measurements and ending with viewing predicted “corrected” response at each measurement position and exporting the filters.
*Room Resonant Modes Acoustic resonances exist in an enclosed space due to sound waves traveling between opposite boundaries. These resonances store energy which takes time to dissipate. This time to dissipate is often called decay time. The image above shows sound decay in a room between 30Hz and 200Hz. Strong resonant modes are visible at 52Hz and 68Hz, with more minor modes at higher frequencies. The image below shows the result of combining the correction filter with the room. The filter precisely matches the time domain behavior of the resonant modes, reducing the room’s excitation at the resonant frequencies. The net result is reduced decay time which is now much more consistent across the frequency range.
**Impulse Response Loudspeakers introduce a time delay that changes across the audio spectrum. This delay is due to the phase shift of crossover networks and the different positions of the acoustic centers of the various drivers employed in a typical multi-way loudspeaker design. The images below show the impulse and step responses of a 2-way horn loudspeaker. Due to the depth of the tweeter horn, the sound from the woofer arrives at the listening position before the tweeter. A properly designed filter can correct this and restore waveform fidelity, most easily seen in the “After” step response (image below). The tweeter and woofer are now seamlessly integrated.
Performing measurements is the first step in generating room correction filters. Focus Fidelity’s impulse response measurement software, Impala, makes this quick and easy. Impala saves the measurements to a single file which users import into Filter Designer, the filter design application.
Using Impala, measurements of the left and right channels are taken at multiple positions. The first measurement users will perform is at the central position. This position is the center (“sweet spot”) of the listening area, with the microphone at the height your ears would be. You should arrange the remaining microphone positions symmetrically around the central 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 for a single-seat listening arrangement.
Key Features (Filter Designer)
Key Features (Impala)
System Requirements
PC Requirements
Audio Hardware Requirements 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. Links to suitable measurement microphones can be found on the Resources page.
Playback Software Requirements Focus Fidelity software generates filters saved as stereo *.wav files. Playback software is required to load these filters and perform the filtering. Suitable applications include Accurate Sound's HLC, Roon, JRiver Media Center, and HQPlayer.
Price
*A license is for a single end-user and may be installed and activated on only one computer at any one time. The license may be deactivated and installed on another computer if required.
For more information on 'Filter Designer' and 'Impala'
About 'Focus Fidelity' (https://www.focusfidelity.com) We create software to advance the state-of-the-art of music reproduction in your home. Our software effectively calibrates audio playback for your loudspeakers and room acoustics, resulting in, quite simply, Higher Fidelity.
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