Monday, February 6, 2017

Audio Reference Gap

Comparing Audio

Let's talk about something that every audio engineer does and is of particular importance in a mixing and mastering context, that's comparing audio. If you are mixing, you may be comparing your mix to a rough mix of the song that was provided or maybe you are comparing to a commercial release. 

In mastering it's critical to compare the mastered version of the song to the raw mix to ensure that the processing steps taken are making an improvement to the mix and essential elements from the mix are retained. The small subtle details are crucial at this stage. 

I've started to use a term recently to describe accuracy issues with comparisons of audio material. This is something I call the Audio Reference Gap.

Audio Reference Gap

The audio reference gap is a gap in process or quality causing inaccuracies with A/B comparisons. The larger the gap, the more inaccurate the comparison.

The reference gap consists of the following items. Timespan, DAC Difference, Level Difference (optional)


Compromises in these areas make it difficult or far too inaccurate to make any reasonable comparison. Why is this important? Well, because decisions made during this process are made off of a skewed perception of the audio.

This has to do with things like the length of time between the comparison or the physical difference of the audio between the comparison (made by different DACs).

Let's take a look at a few of these areas in more depth.

Timespan

The length of time between comparisons is critical to the accuracy of that comparison. The human brain doesn't have the capacity to remember details of an audio comparison beyond about a second. The more subtle the difference the closer together the comparison should be. This means that if someone were to listen to audio, get up and patch a piece of equipment in and listen again, they wouldn't perceive any of the details of that comparison. Sure, if something is so stark in contrast that it's overwhelming that may be perceived, but we are talking about being able to recognize details, even minute details while performing audio processing tasks.  

The timespan of the comparison should be kept as short as possible and well under the 1-second mark for critical comparisons.

Monitoring Path Difference

Differences in the monitoring path can have a pretty large difference in the way that two pieces of audio are perceived. The monitoring path consists of everything from your Digital to Analog Converter (DAC) to your ears. 

Comparing audio through two different DACs adds problems to the comparison. Not all DACs are created equal and different specifications, converter chips, components in the signal path can affect the audio in various ways.

One DAC may be clear and punchy, and the other may be less clear and have problems with low-end focus. So if you are comparing a mix or master, you may be making adjustments to the audio that are unnecessary or have a negative impact. 

Mastering is all about subtleties so even if two different DACs are both excellent and nearly identical they are still different and compromising your comparison.

Level Difference (Optional)

We all know that level difference can fool us into believing one piece of compared audio is better just because it is louder. The reason I added this as optional is that there may be times when you are comparing audio when you want to know about the level difference. 

Better Comparisons

The point of all of this is to reduce the reference gap and remove as many obstacles as possible. This will put you on the path to working better and making better audio decisions in all of your processing tasks.

The timespan should be kept as short as possible to ensure your perception of the material is as accurate as possible. This span should be well under the 1-second mark preferably to where it feels like it's instantaneous. A good monitoring controller is essential for this and will vastly improve your workflow.

The same DAC should be used for all A/B comparisons. This way inconsistencies won't cause you to make inaccurate processing decisions. I can't stress enough the importance of having good digital to analog converters. Since every decision in recording, mixing, and mastering (assuming digital audio is involved) is based on your DAC.

Lastly, if level difference isn't something you are comparing in your A/B, then you are going to want to make sure you level match the material you are comparing. This will allow for a more reasonable comparison and not get fooled by the louder version.

Hopefully, this gives some food for thought while you are performing your critical audio tasks or considering purchases for your studio. Your workflow and audio quality will thank you. 

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