Linear Phase EQ

The high-quality Linear Phase EQ effect is similar to the Channel EQ, sharing the same parameters and eight-band layout. The Linear Phase EQ uses a different underlying technology, however, which perfectly preserves the phase of the audio signal. This phase coherency is assured, even when you apply the wildest EQ curves to the sharpest signal transients.

A further difference is that the Linear Phase EQ uses a fixed amount of CPU resources, regardless of how many bands are active. The Linear Phase EQ also introduces greater amounts of latency. Therefore, it is strongly recommended that you use it for mastering previously recorded audio and avoid using it when you are playing software instruments live, for example. The latency compensation feature of Logic Pro can be helpful when you are using this effect.

Tip: The parameters of the Channel EQ and Linear Phase EQ are identical, enabling you to freely copy settings between them. In Logic Pro, if you replace a Channel EQ with a Linear Phase EQ (or vice versa) in the same insert slot, the current settings are automatically transferred to the new EQ.

Linear Phase EQ Parameters

The left side of the Channel EQ window includes the Gain and Analyzer controls. The central area of the window includes the graphical display and parameters for shaping each EQ band.

Figure. Linear Phase EQ window.
Linear Phase EQ Gain and Analyzer Controls
  • Master Gain slider and field: Sets the overall output level of the signal. Use it after boosting or cutting individual frequency bands.
  • Analyzer button: Turns the Analyzer on or off.
Linear Phase EQ Graphic Display Section
  • Band On/Off buttons: Click to turn the corresponding band on or off. Each button icon indicates the filter type:

    Band 1 is a highpass filter.

    Band 2 is a low shelving filter.

    Bands 3 through 6 are parametric bell filters.

    Band 7 is a high shelving filter.

    Band 8 is a lowpass filter.

  • Graphic display: Shows the current curve of each EQ band.
    • Drag horizontally in the section of the display that encompasses each band to adjust the frequency of the band.

    • Drag vertically in the section of the display that encompasses each band to adjust the gain of each band (except bands 1 and 8). The display reflects your changes immediately.

    • Drag the pivot point in each band to adjust the Q factor. Q is shown beside the cursor when the mouse is moved over a pivot point.

Linear Phase EQ Parameter Section
  • Frequency fields: Adjust the frequency of each band.
  • Gain/Slope fields: Set the amount of gain for each band. For bands 1 and 8, this changes the slope of the filter.
  • Q fields: Adjust the Q or resonance for each band—the range of frequencies around the center frequency that are affected.

    Note: The Q parameter of Band 1 and Band 8 has no effect when the slope is set to 6 dB/Oct. When the Q parameter is set to an extremely high value (such as 100), these filters affect only a very narrow frequency band, and can be used as notch filters.

  • Link button: Activates Gain-Q coupling, which automatically adjusts the Q (bandwidth) when you raise or lower the gain on any EQ band, to preserve the perceived bandwidth of the bell curve.
  • Analyzer Mode buttons (Extended Parameters area): Choose Peak or RMS.
  • Analyzer Decay slider and field (Extended Parameters area): Adjust the decay rate (in dB per second) of the Analyzer curve (peak decay in Peak mode or an averaged decay in RMS mode).

Using the Linear Phase EQ

The Linear Phase EQ is typically used as a mastering tool and is, therefore, generally inserted into master or output channel strips. The way you use the Linear Phase EQ is obviously dependent on the audio material and what you intend to do with it, but a useful workflow for many situations is as follows:  Set the Linear Phase EQ to a flat response (no frequencies boosted or cut), turn on the Analyzer, and play the audio signal. Keep an eye on the graphic display to see which parts of the frequency spectrum have frequent peaks and which parts of the spectrum stay at a low level. Pay particular attention to sections where the signal distorts or clips. Use the graphic display or parameter controls to adjust the frequency bands as desired.

You can reduce or eliminate unwanted frequencies, and you can raise quieter frequencies to make them more pronounced. You can adjust the center frequencies of bands 2 through 7 to affect a specific frequency—either one you want to emphasize, such as the root note of the music, or one you want to eliminate, such as hum or other noise. While doing so, change the Q parameter(s) so that only a narrow range of frequencies are affected, or widen it to alter a broad area.

Each EQ band has a different color in the graphic display. You can graphically adjust the frequency of a band by dragging horizontally. Drag vertically to adjust the amount of gain for the band. For bands 1 and 8, the slope values can be changed only in the parameter area below the graphic display. Each band has a pivot point (a small circle on the curve) at the location of the band’s frequency; you can adjust the Q or width of the band by dragging the pivot point vertically.

You can also adjust the decibel scale of the graphic display by vertically dragging either the left or right edge of the display, where the dB scale is shown, when the Analyzer is not active. When the Analyzer is active, dragging the left edge adjusts the linear dB scale, and dragging the right edge adjusts the Analyzer dB scale.

To increase the resolution of the EQ curve display in the most interesting area around the zero line, drag the dB scale, on the left side of the graphic display, upward. Drag downward to decrease the resolution.

Using the Linear Phase EQ Analyzer

The Analyzer, when active, makes uses of a mathematical process called a Fast Fourier Transform (FFT) to provide a real-time curve of all frequency components in the incoming signal. This is superimposed over any EQ curves you have set. The Analyzer curve uses the same scale as the EQ curves, making it easy to recognize important frequencies in the incoming audio. This also simplifies the task of setting EQ curves to raise or lower the levels of frequencies or frequency ranges.

The bands derived from FFT analysis are divided in accordance with the frequency linear principle—there are more bands in higher octaves than in lower ones.

As soon as the Analyzer is activated, you can change the scaling with the Analyzer Top parameter, on the right side of the graphic display. The visible area represents a dynamic range of 60 dB. Drag vertically to set the maximum value to anywhere between +20 dB and −40 dB. The Analyzer display is always dB-linear.

Note: When choosing a resolution, be aware that higher resolutions require significantly more processing power. High resolution is necessary when trying to obtain accurate analysis of very low bass frequencies, for example. It is recommended that you disable the Analyzer or close the Linear Phase EQ window after setting the appropriate EQ parameters. This will free up CPU resources for other tasks.