Graphs Settings

Configure display options and graph behavior.

Display

Plot Resolution

Options: 16k points, 32k points, 64k points
Default: 32k points (balanced)

FFT resolution for frequency response computation.

• 16k points (16384): Faster computation, lower frequency resolution
• 32k points (32768): Balanced performance and resolution
• 64k points (65536): Maximum frequency resolution, slower computation

Impact:

• Higher resolution provides finer low frequency detail in magnitude, phase, and group delay plots
• Affects computation time for filter responses and driver measurements
• Does not affect the actual filter quality, only the analysis resolution

Steep Crossover Smoothing

Options: Enabled, Disabled
Default: Enabled

Reduces smoothing near crossover frequencies to reveal steep filter slopes in magnitude plots.

How it works:

The strength of the smoothing reduction is proportional to the filter’s effective acoustic slope:

The transition is progressive: smoothing is gradually reduced within ±0.5 octave around the crossover frequency, reaching the minimum at Fc itself.

When enabled:

• Steep crossovers (LR6 / 36 dB/oct and above) receive full reduction — smoothing drops to 1/96 octave at Fc
• Common crossovers (LR4 / 24 dB/oct) receive an intermediate reduction of ~67 %
• Shallow crossovers (LR2 / 12 dB/oct and below) are left unchanged — the filter slope is gentle enough to be visible without smoothing reduction
• Brickwall FIR always use full reduction (safe default)
• Only affects magnitude display curves — does not modify phase, group delay, or filter generation

When disabled:

• Uniform smoothing is applied across the entire frequency range
• Provides consistency with external measurement tools that use constant smoothing

Note: External measurements with uniform smoothing will show gentler crossover slopes compared to LinFIR’s steep-crossover mode. This is expected — the adaptive reduction reveals the true filter response near crossovers.

Group Delay & Phase Truncation

Optionally truncate group delay and phase curves to the active frequency region using magnitude thresholds.

Enable Truncation

Default: Enabled

When checked: Group delay and phase curves are shown only where the corresponding magnitude exceeds a threshold below the maximum.

When unchecked: Full-range phase and group delay displayed regardless of magnitude.

Purpose:

• Avoid displaying phase/group delay in stop-band regions
• Focus on pass-band characteristics
• Reduce visual clutter from irrelevant frequency ranges

Truncation Thresholds (dB below maximum)

Independent thresholds for different contexts:

How thresholds work:

• Values are expressed as dB below the maximum magnitude in the reference curve
• Example: -20 dB means “show phase/GD only where magnitude > (max - 20 dB)”
• Adjustable range: -120 dB to -20 dB

Context matching:

• The reference magnitude matches the context
• Example: FIR curves use FIR magnitude as reference
• Drivers use driver magnitude as reference

THD Truncation:

• Only available for Drivers context
• Shows Total Harmonic Distortion only in active magnitude regions

Magnitude Plot Bounds

Configure default Y-axis bounds for magnitude plots.

Drivers Range (dB)

Range: 20 to 200 dB
Default: 60 dB

Y-axis range for speaker magnitude plots.

• Calculation: From (max_response - range) to (max_response + 5 dB)
• Smaller values (20-40 dB): Zoomed view, emphasizes small variations
• Moderate values (60-80 dB): Good balance for most designs
• Larger values (100-200 dB): Wide view, shows full range

Filters Lower Bound (dB)

Range: -200 to 0 dB
Default: -100 dB

Lower bound of Y-axis for filter magnitude plots (IIR, FIR, FIR+IIR).

• Higher values (-40 dB): Focuses on pass-band details
• Lower values (-100 to -200 dB): Shows deep stop-band attenuation

Impulse/Step Response Display

Adaptive display automatically detects and shows only the relevant portion of impulse and step responses.

Enable Adaptive Display

Default: Enabled

When checked: Automatically detects signal boundaries based on amplitude threshold.

• Detection threshold: 1/1000th of peak amplitude
• Automatic margins: Adds configurable time before and after detected signal

When unchecked: Always shows the complete impulse response (full tap length).

Use case: Focuses view on active signal portion, especially useful for long impulse responses with significant zero-padding.

Margin Before (ms)

Range: 0 to 50 ms
Default: 5 ms

Time added before detected signal start.

Purpose: Ensures pre-ringing or early arrivals are visible in the plot.

Margin After (ms)

Range: 0 to 100 ms
Default: 10 ms

Time added after detected signal end.

Purpose: Captures decay tail and late reflections.

Focus on Summed Response

Default: Disabled

When enabled in multi-driver plots:

• All curves (individual drivers and sum) use the summed IR time boundaries
• Focuses on the main energy region of the system response

When disabled (default):

• Uses the union of all individual curve boundaries
• Shows the full extent of all driver responses

Use case: Quickly identify timing alignment issues across speakers by focusing on the system sum.

Response Overlays

Show Listening Window Curve

Default: Enabled
Requires: A valid LinFIR license

Displays the Listening Window curve in the frequency graph when in Drivers/Measurements mode and off-axis measurements are available. The curve appears in the graph legend as “LW”.

The Listening Window is the spatial average of responses within ±30° horizontal and ±10° vertical. See System Processing for details.

Note: This option is disabled when no valid license is present. The toggle is grayed out and the curve is not displayed.

Show Raw Response When Filter Windows Are Open

Default: Enabled
Requires: A valid LinFIR license

When enabled, a dashed overlay of the unfiltered (pre-filter) driver response is drawn on the frequency, phase, and group delay graphs whenever a filter window is open for that driver.

Which windows trigger the overlay:

• Per-driver: LP, HP, correction FIR, or IIR filter window
• Global: Global FIR correction or Global IIR filter window (shows the unfiltered sum/average)

What is shown:

• The response before any FIR or IIR filter is applied to that driver — the raw impulse response processed only through gain and windowing
• The overlay is colored to match the driver’s curve color, drawn as a thin dashed line
• For the global sum, the overlay is drawn in white (dark mode) or black (light mode)

Use case: Immediately see how much correction a filter is applying, without disabling filters. Useful for validating crossover slopes, EQ depth, and phase shaping against the unprocessed baseline.

Note: This option is disabled when no valid license is present. The toggle is grayed out and the overlay is not displayed.

Settings Summary Table

Performance Considerations

Real-Time Filter Processing Architecture

LinFIR differs fundamentally from traditional FIR filter design software in how it processes and displays results.

Real-time (“online”) filter generation:

• Filters are generated and applied to driver impulse responses in real time based on UI interactions
• The complete signal processing chain is computed immediately as you adjust parameters
• You see the true response of the entire filter chain instantly, including all windowing artifacts and actual behavior

Why this matters:

• Immediate feedback: No “generate” or “apply” button required - changes are visible instantly
• Transparency: Shows exactly what the filters can and cannot do, with all artifacts visible
• Accuracy: No approximation or preview mode - what you see is what you get

Contrast with traditional software:

• Most FIR design tools require you to validate parameters before showing the true response
• They often show theoretical or idealized responses that don’t reflect actual implementation artifacts
• LinFIR prioritizes showing real-world behavior over computational convenience

Filter Application Methods

FIR filters:

• Applied via fast convolution (multiplication in Fourier domain)
• Highly efficient for typical filter lengths
• Computational cost scales with filter length and number of measurements

IIR filters:

• Applied via recursive difference equations (time-domain processing)
• Extremely efficient regardless of filter complexity
• Minimal performance impact even with many cascaded sections

Performance Impact Factors

Filter length:

• Filters up to 4096 taps: Negligible performance impact on modern CPUs
• Filters 4096-8192 taps: May cause slight delays on slower systems
• Filters >8192 taps: Can noticeably slow down the application, especially during interactive adjustments

Off-axis measurements:

• Each off-axis measurement requires the full filter chain to be recomputed
• Projects with many off-axis angles and long filters may experience longer update times
• LinFIR prioritizes UI responsiveness using background processing (see below)

Background Processing for Responsiveness

To maintain smooth UI interaction even with complex projects, LinFIR uses processing prioritization:

Priority processing (synchronous, immediate):

• On-axis measurement (0°, 0°): Always computed first in the main thread
• Currently displayed angle: Computed immediately for instant visual feedback
• Filter parameters: Updated in real-time as you adjust controls

Background processing (asynchronous, non-blocking):

• Remaining off-axis measurements: Computed in a background thread after priority angles
• Directivity index: Calculated asynchronously when all measurements are ready
• System sum calculations: Processed in parallel when multiple drivers are active

User experience:

• Main graph updates are always immediate - you see changes to the selected angle instantly
• UI remains fully responsive even during heavy background computations
• You can continue adjusting parameters while background calculations complete

Optimization Recommendations

For slower systems or very long filters (>8192 taps):

1. Reduce plot resolution: Settings → Graphs → Plot Resolution

   • Default: 64k points (maximum quality)
   • Recommended for performance: 16k or 32k points
   • Performance improvement with minimal visual quality loss

2. Disable clipping detection: Settings → General → Filter Processing

   • Eliminates test signal processing on every update
   • Only disable if you’re confident in your gain staging

3. Limit off-axis measurements:

   • Use reasonable angle increments (10 or 15°)

Performance is always optimal for:

• Projects with standard filter lengths (≤4096 taps)
• IIR-only filtering (always fast regardless of complexity)
• Single on-axis measurements
• Modern multi-core processors (2020 or newer)

Best Practices

Performance Optimization

• Slower systems: Reduce plot resolution to 16k or 32k points
• Complex projects: Consider disabling clipping detection if filters are well-understood

Filter Design

• Auto Causal Alignment: Keep enabled unless you need precise manual control over IR positioning
• Show Manual FIR Delay Compensation: Keep disabled unless you are experienced in signal processing and need manual FIR alignment control
• Clipping Detection: Keep enabled during design, test actual content before deploying

Graph Display

• Truncation: Enable for cleaner phase/GD plots focused on active frequency regions
• Focus on Summed Response: Enable when analyzing multi-driver timing alignment

Measurement Setup

• Sweep Duration: Use 5-7 seconds for full-range, 2-3 seconds for limited bandwidth
• Sweep Level: Adjust based on amplifier sensitivity (-12 to -6 dBFS typical)