How To Listen Critically

Critical listening is an important skill for sound engineers & artists of all kinds. In this compendium of tips, I focus on critical listening for more "analytical" purposes, rather than more "creative" purposes. I present ideas for critical listening that may be useful in contexts such as:

• Mixing a song
• Mastering an album
• Fixing problems in recorded material
• Identifying issues in a musical system like a live rig or a modular synthesizer patch

Critical listening is also required in a variety of creative contexts, such as critiquing the musicality of recorded performances. Hopefully, some of these tips are useful in those contexts, too. But my main focus is on ways to hear technical problems.

Prerequisites

Before you try to listen critically, it's most helpful if you:

• Know your listening system.
• Have a quiet background. Don't try to listen critically while you ride a train.
• Have a "good enough" listening system. For example, it's hard to hear problems in the bass if you are listening on phone's built-in speaker.
• Make time and space for critical listening.

Tools

The most important tools for critical listening are your ears and your brain. Here are some additions that may be useful:

• A variety of listening systems: Conventional wisdom in music production is to check how well a mix "translates" between listening systems. Possible alternative listening systems include:
  
  • Near field monitors
  • Ear buds
  • High quality headphones
  • A Bluetooth speaker
  • Car stereo
  • iPhone speaker
  • Laptop speaker
  Note that headphone-based systems are substantially different to speaker-based systems, especially for spatial imaging. Room characteristic and treatments play a big role, too.
• Trusted reference tracks: Everyone has their favorites. The main thing is that you know the music and the sound very well on a range of systems, and that you admire the production. Try out others' suggestions here and see what you like. For about ten years, my reference tracks have been "Rods and Cones" by Blue Man Group and "Right in Two" by tool.
• Analytical music software tools: Match EQ in Logic Pro is good for taking EQ differences out of the equation, both to help you focus on other aspects and to fix problems. Spectrum analyzers can be helpful sometimes. The spectrogram view in Audacity also has its uses. Python + numpy + matplotlib (or MATLAB) is the most flexible (and difficult) approach. This opens the big, related topic of visualization and analytical qualification.
  

Approaches

Critical listening is listening plus critical thinking. Everything that you know about critical thinking ought to be applied to your critical listening. Here are some tips based on my reading and experience:

• Focus: What problems are you listening for?
• Anti-focus: What problems may exist that you are not listening for? Try to see the forest for the trees.
• Repetition and fatigue: Some problems elude the first hearing or require many subtle comparisons. This gets boring and tiring -- sometimes fast! One strategy is to listen over and over, form an opinion (take notes!) then stop for a long break. After the break, listen again and see if you feel differently. The long break might be an hour, or until the next morning, or it could be 6 months. 
• Contrasts and background: We hear differences and rapidly become acclimatized to similarities. Often it's easy to determine which of two options is better with a systematic, direct AB test. Also, you can try to reset your background expectations by listening to alternative sounds. This could be your favorite reference tracks played back on the same system or it could be a familiar quiet acoustic scene like the hum of your fridge (and nothing else) while you have a coffee. Another option is the sound of city traffic when you go for a walk. My ideal break from critical listening would be a walk through a quiet forest with a small stream and birdsong.
• Sleep makes for a good break. Sleep is typically an extended period of silence or quiet. The "morning person" vs. "night person" dimension of your personality may or may not correspond to the best time for you to listen critically. Sleep also helps reset critical thinking -- which emphasizes the importance of taking detailed and specific notes -- tomorrow morning you may hear and think an entirely different thing! Critical listening is, therefore, hard to rush.
• Level makes a big difference. Keep in mind that people tend to like the louder of two options. Louder also fatigues you faster. (Brighter is like louder.) Our ears' frequency sensitivity depends highly on level: we hear more bass at loud volumes (refer to the Fletcher-Munsen equal loudness curves). One approach is to use Bob Katz's K12 metering system. [Note to self: Look this up and, if possible, try it out.] You can get SPL phone apps, e.g. NIOSH SLM. Level calibration is harder on headphones. 
• "Hearing around corners:" This is less analytical critical listening and more of a creative act. Sometimes you hear different and surprising aspects of a sound in different contexts. Different and limited listening systems is one approach here, also:
  
  • Listen in the bath (water running or not).
  • Listen while falling asleep or meditating.
  • Listen while kids are yelling.
  • Listen while simultaneously playing back The Beatles.
  • Listen very quietly. (Sometimes you can even hallucinate interesting things in this way!)
  • Listen to tracks soloed. If it's not your song, then try to get the stems. 
  • Reverse it and listen to that. 
  • Slow it down 2x and listen to that. 
  Many other ideas are possible here; this is an interesting topic in its own right.
• Know yourself and your own limitations -- but also aim to grow in ways that matter to you. People aren't born with "golden ears;" they learn to be good critical listeners. Having "golden ears" isn't some kind of either-or thing; we are all on a journey and we all can have well-reasoned and informed opinions. We all ought to draw on each other's experience and expertise. If you know someone whose taste and judgement you highly respect, then try to learn from them. Listen to material together and try to hear the subtleties that they hear.
• Check the solution: You had a song, you listened critically, you found a problem, now you think have fixed it. You need to listen critically again, and even compare before and after. Blind testing is useful here, like an ABX test. There are plug-ins to help with this. Also, you can get a second opinion from someone whose judgement you trust. The industrial-strength solution here is to do a statistical study in controlled conditions with numerous (like >30) listeners. However, running listening studies is an art unto itself, for example, do you use expert golden-eared listeners, or naïve members of the public?
• Know when the solution is good enough. Perfect is the enemy of good, but so is mediocre. Have high standards, and keep the alternative in mind. For example, if you can't fix this problem in a mix, then do you simply not release the song? Maybe it's better to release the song if it's strong musically -- or maybe you can afford to re-record the problem section.
  

Conclusion

I presented a variety of tips and strategies to help with the art of critical listening for analytical purposes. Critical listening is an art and a skill. Critical listening is grounded in critical thinking. Having good equipment helps, but experience, skill and tenacity are more important.

Post script

Keep your ears in good health. For me, this means that I need to regularly ensure that my ears aren't filling up with wax.