Linear Phase EQ: The Difference, How & When To Use It!

Linear Phase EQ: The Difference, How & When To Use It!

A linear phase EQ is a special type of equalizer that aims to apply equalization without introducing phase shift or altering the timing of the audio signal in the frequency domain. To fully understand it, let's break down the concepts involved:

1. Phase Shift and Traditional EQs

In a traditional (non-linear phase) EQ, when you boost or cut certain frequencies, the phase of the audio signal is altered. Phase refers to the timing relationship between different frequency components of a sound wave.

  • Phase shift happens when different frequencies in your signal are delayed by different amounts, which can lead to certain sonic changes like smearing, distortion, or a loss of clarity.
  • In many cases, these changes are subtle, and in certain types of music or sound design, phase shifts may not be noticeable or problematic.

However, in some contexts—especially when working with complex material or when processing multiple tracks together—these phase shifts can cause undesirable changes in the sound. For instance, if you boost a certain frequency on a guitar, the phase shift could cause it to sound less clear or lose its punch.

2. Linear Phase EQ

A linear phase EQ works differently. It tries to prevent phase shift by applying equalization in a way that maintains the phase relationships between frequencies. This means that all frequencies are affected equally in terms of timing (or phase), so the relative timing between different frequency components remains intact.

  • Phase relationship preserved: When you apply a boost or cut with a linear phase EQ, it tries to maintain the alignment of the waveform’s different frequency components, so the sound remains more transparent and natural.
  • Prevents time-based artifacts: Because the phase remains intact, linear phase EQs don't cause time smearing or distortion like traditional EQs can. This makes them particularly useful in mixing and mastering when you need to maintain clarity and precision.

3. How Does It Work?

A linear phase EQ works by using a minimum phase shift filter in a different way than traditional EQs:

  • It processes the audio in the frequency domain and uses algorithms that introduce a delay across all frequencies in a way that keeps their relationships intact. This delay happens equally across all frequencies, meaning there’s no variation in phase between them.
  • While traditional EQs work in the time domain (adjusting the waveform directly), linear phase EQs involve Fourier Transform techniques to analyze and modify the signal in the frequency domain, then convert it back to the time domain without introducing phase shifts.

4. When to Use a Linear Phase EQ

  • Mastering: In mastering, it's crucial to avoid any unwanted artifacts or phase shifts, as you're dealing with the final mix. A linear phase EQ can ensure that the tonal balance of the track is preserved without introducing any phase-related distortion.
  • Multitrack Mixing: If you’re processing multiple tracks together, especially when they have overlapping frequencies (e.g., vocals and guitars in the same range), a linear phase EQ can help avoid phase cancellation and other artifacts.
  • Critical Audio Work: If you're working with something that requires extremely precise frequency control, such as removing specific resonant frequencies without altering the overall character of a sound, linear phase EQs are ideal.

5. Downsides of Linear Phase EQ

While linear phase EQs are great for maintaining clarity, they have some downsides:

  • Latency: Because they work by introducing a delay across the entire frequency spectrum, linear phase EQs often introduce latency (a small time delay). This can be an issue when mixing in real-time or when using many linear phase EQs on several tracks at once.

  • Pre-ringing Artifacts: A common issue with linear phase EQs is pre-ringing. This is a type of artifact where the audio appears to “ring” before a transient (like a snare hit) occurs. It happens because the filter is trying to adjust frequencies in a way that’s phase-neutral, but this can cause an unnatural “smearing” of the attack of sounds.

    • Pre-ringing is more noticeable on sharp transients (like percussion or plucked strings). In these cases, a minimum-phase EQ (a non-linear phase EQ) might be a better option since it can handle transients more naturally without introducing pre-ringing.

6. Summary

  • Linear Phase EQ: A type of equalizer that preserves the phase relationships between frequencies, resulting in a more transparent sound without time-based distortion or phase shifts.
  • Best for: Mastering, multitrack mixing, and other situations where precision and clarity are crucial.
  • Downsides: Can introduce latency and pre-ringing artifacts, especially with sharp transients.

In most mixing scenarios, traditional EQs are often used because they’re more "musical" in the way they handle phase and transients. However, for critical applications where you want to preserve every detail and avoid artefacts, a linear phase EQ can be an essential tool in your mixing and mastering toolbox.

By the Stealify Team! 

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