Rob from B Double E holding an ipad with audio samples before and after compression.

What is compression and do voiceovers need it?

Compression is a topic that confuses many and strikes fear into the hearts of many. Yet people like me insist on banging on about how important it is, and insisting that voice overs should at least try to get their heads around the topic. So in this first blog of 2, I’m going to explain what compression is and why it’s so important.


Compression is confusing

Wind the clock back to the late 90s when I was at college training to be a sound engineer and compression was a big part of the course. There were 30 – 40 of us in my class and when compression was first explained to us there were only 3 or 4 people who understood it the first time. This was a room of people tech-minded enough to consider a career in sound engineering. I was one of those 3 or 4 people (cue a chorus of people shouting ‘Of course you were!’).

I tell this story simply to reassure you that if you find it difficult getting your head around the topic, it’s not a surprise. Keep trying and keep reading and hopefully, by the time you’ve read this, it’ll make more sense.

Also just to note that I’m talking about audio compression here, not data compression. Yes, they are 2 totally different things that are both called compression. I explain the differences in this blog. Told you it’s confusing!


A brief history of compression

Hardware compressors were invented in the 1930s for use in the broadcast industry to prevent over-modulation in radio broadcasts. They did this by ensuring the signal to be broadcast didn’t get too loud. The usefulness of this was realised by the developing recording industry, and as recording studios developed compressors were incorporated into the kit found within, and the technique was refined and developed for recording applications.

It was necessary to compress audio getting pressed onto vinyl to make sure the audio signal levels didn’t fall below the noise floor or get so loud it would cause the needle to jump. When magnetic tape was invented and became more widely used compressors were used as things were recorded for the same reasons. Classical music in particular can have a very wide dynamic range – up to 50 or 60dB – whereas good quality 2” tape has a dynamic range of 40 – 50dB.

As recording developed further, compression became a creative tool as well as a practical one. Now we have digital recording it’s less necessary to compress as we record (16-bit systems have 96dB dynamic range) but we still use compression as we mix and master our audio.


What does a compressor do?

As we’ve seen above, compressors squash the dynamic range of a recording so the difference between the loud bits and the quiet bits is smaller. A compressor constantly monitors the levels and makes millisecond by millisecond adjustments to the volume (depending on the settings) to keep the volume more even.

This can make a piece of audio easier to listen to, and even easier to hear. It helps us place different components of a mix exactly where we want them to be, and can give audio a more aesthetically pleasing and polished sound.

People often think that compressors make everything louder. They actually don’t. the compression process makes audio quieter overall, but there’s usually a volume knob on a compressor that turns the output levels up to compensate for the compression effect.


Why should a voiceover use compression?

Completing a mix without using any compression can be an extremely difficult (and pointless) thing to do. As stated above compression helps mix components sit where you want them to. There may well still be some automation of levels needed to get the mix sounding as you want to, but it’s considerably less than it would be if you try to mix without compression. You simply can’t get the fidelity and the clarity in the voiceover needed in a mix without it. Much of the copy would be lost behind the music and SFX and the result would be scrappy.

Fair enough, but what about dry voice? Firstly compression adds a tightness and polish to the sound, so the finished product just sounds better. But also consider that voice over you’ve done and where it’s going to be used in the wild. Maybe you’ve recorded some announcements for a website, auditorium or shopping mall. The recordings will be played over the noise and hubbub of the office or the comings and goings of the general public. So that need to ‘place’ the audio like you would in a mix is still relevant. Making the recordings you do as clear and easy to listen to as possible makes them much more useful in the wild.

Take a listen to the below audio and you’ll see what I mean. This is a chunk of audio that is uncompressed, then a compressed version of the same.


The problem with compression

The big problem with compression is that it can be hard to get your head around, and therefore it can be difficult figuring out how to use it properly. I would argue that badly compressed audio is worse than uncompressed audio, so would probably say that until you have a decent handle on how to use a compressor you’re probably better off without it.

So how do you set and use a compressor?

We’ll have a look at that next time.


If you’re looking for help improving your compression and editing skills, I can help with customised 1-2-1 audio training. Get in touch and we can put together a tailored training plan.

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