Mastering 101 : Compression

Every Monday, we will be looking at one of these mastering topics, if you missed it, click on the topic below to catch up:

  1. What is mastering?
  2. Signal Flow & Metering
  3. EQ
  4. Compression
  5. Limiting
  6. Preparation

This week, we look at Compression.

There are plenty of tutorials and articles out there about compression, what it is and what it isn’t. This week, we are going to focus specifically on compression for mastering and how we can approach it as you D.I.Y your own masters.


Know What a Compressor Does

  • A compressor reduces the dynamic range of a mix. This means the difference between the loudest and softest parts of your mix would be less resulting in mix with lesser dynamics and movement. The trade off here is that, with a lesser dynamic range, you can push the mix louder by compressing.
  • That matters in mastering. Compression can do many other things like make something more punchy, increase detail or make things sound fuller, but in mastering a compressor makes things louder.
  • Although mastering engineers use limiters to make mixes louder, solely using a limiter to do all the legwork will produce unwanted effects such as pumping and distortion. But splitting the work between a compressor and limiter would yield a more natural result.

Does The Mix Need Compression?

  • About 80% of the mixes now come in so hot and slammed that you a compressor is not required. Use your ears when you get a mix, if you find that the mix itself is already pretty compressed, adding mastering compression probably wouldn’t help it much.
  • Getting hold of a Dynamic Range meter such as Brainworx’s bx_meter will help you calculate the dynamic range of your mix / master. The lower the number, the less dynamic.


How Much Compression?

  • In truth, mastering engineers hardly use any compression. Even if they do, it is at low ratios and high thresholds.
  • Here’s some general guidelines, if you want to use compression while mastering:
    • Start your ratio at 1.25:1 or 1.5:1. Going past a ratio of more than 2:1 is not recommended.
    • Set your threshold pretty high so that you are getting at most 2dB of gain reduction.
    • Use your ears! If you apply compression and do not like how it changes your master, take it out!
    • Keep asking yourself after every move – “Am I making the music sound better?”

Multi-Band vs Single-Band Compression

  • Pros of a multi-band:
    1. Isolated Individual Bands Across Frequencies.
      • As you know, compressors react differently to different frequencies. For example bass frequencies are longer in wavelength and having a band to process the low-end without affecting the rest of the frequencies is ideal.
    2. Use Different Settings across Different Bands:
      • With a multi-band compressor, you can set different attack, release and threshold settings for the different bands. You can divide the frequency bands into 3 or 4 bands (low, low-mids, mids and highs)
    3. Tailoring Compression to your Program Mix
      • Because multi-band gives you the ability to set different settings for each band, you are essentially tailoring your compression specifically for your mix.
  • Cons of a multi-band:
    1. Many Bands can be Your Enemy Too
      • For a multi-band to work, a plug in needs to use crossover filters to separate your audio into different bands. Anytime you run audio through a filter, you lose a little bit of fidelity. It adds a little bit of ringing, noise and distortion.
    2. Over Processing can Mess Things Up
      • With mastering, the number one rule is not to over process. Over processing of a multi-band comp can easily skew the frequency and phase of your master and cause it to lose fidelity. I would recommend only using a multi-band compressor if you really know what you’re doing.

Summing it Up

  • Compression can be a useful tool, if your ears tell you that the mix needs it.
  • Make use of M/S processing to perhaps tame a vocal in a mix if you think it is too dynamic.
  • Work in moderation. Try not to over process and keep the gain reduction to not more than 2dB.

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February 22, 2016

Reuben Raman Product Marketing Manager at Splice