Doing what I do for a living I get to hear a fair amount of audio that voiceovers have recorded in their home studios. The standard I receive can vary, sometimes the levels are a bit too low/high, sometimes the room isn’t as well treated as it could be. But there is one thing that recurs over and over again that would really improve the quality of the recording – the use of a high pass filter.
So here we go VOs. My guide to what a high pass filter does and why you should be using one. Now I know that when you get your brief from your client they ask for un-processed audio, so you sent them exactly that – you record the script, you may edit it (depending on the client and the brief – you almost certainly take out the fluffs, burps and sneezes) and you send it off. You certainly don’t add compression or EQ. But in my opinion, although a high pass filter (HPF) is technically an EQ process it doesn’t count. By using one you will tighten up the audio you send and help it sound more professional. Your client won’t notice that you’ve applied it (if you apply it properly) but may well notice if you haven’t.
Look for the little funny tick
So what is a high pass filter and what does it do? We need to take a step back first to explain it properly. Sound is a form of energy – you may call it acoustic energy but physicists would probably call it kinetic energy. So a sound wave possesses energy which it passes on as the wave spreads. As it spreads it loses energy and the sound dies away. High frequency sounds have less acoustic energy than low frequency sounds – I’m sure at some point you’ve heard your neighbours playing their music coming through your walls; it’s the bass frequencies that come through and you hear the boom boom boom of the kick drum keeping you awake until 4 IN THE BLOODY MORNING! Higher frequencies simply don’t have the energy to pass through the walls. With this in mind, it’s always going to be the bottom end frequencies that take a greater effort to ‘tame’ in any recording environment.
A high pass filter attenuates bottom end frequencies by increasing amounts the lower they are, so by applying a high pass filter to your recordings you can hugely reduce the very low frequency sounds that may otherwise mar your recordings – the rumble of the main road 3 streets away or the occasional lorry passing your window, the washing machine going into a spin cycle 2 floors down, the person walking across the floor in the next room who’s managing to vibrate the floorboards enough to transmit the vibrations up your mic stand. It can help no end in lowering the noise floor in your studio, making it seem quieter than it is.
Plus there are other considerations – your voice and your mic! If you’ve taken advice on which mic you bought as your voicing mic you probably bought a mic with a cardioid response – ie it picks up your voice from the front and sides but not the back. It’s a good choice of mic as rejecting sound from the back makes it much less likely to pick up unwanted sound sources. Except that all mics other than omnidirectional mics are subject to what’s called the bass proximity effect. Simply put, this is where the bass frequencies are boosted when the sound source is very close to the mic. You will no doubt have been taught that the best place to voice from is close up to your mic thereby increasing the amount of unwanted bottom end on your recordings. Using a HPF really can clean up a lot of this extra bass that you add by utilising good practice. Plus it can clean up a lot of the bottom on pops caused by plosive Ps and Bs.
Still worried that your client wanted unprocessed audio? Don’t be. The frequencies that a HPF works on are below the frequencies that naturally occur in the human voice so the program material that your client wants will be untouched by cleaning up the audio with a HPF.
Good in theory, but what about actually in practice ? Glad you asked. Here we go –
Here is me reading a bit of Gullivers Travels. It’s not a very good read because I was trying to accentuate the above issues. It’s unedited and unprocessed. You’ll hear some ‘silence’ (actually me stomping around a floor below my studio) and then the read. There is an undercurrent of bottom end which makes the read sound ‘scruffy’
so now for exactly the same piece of badly read audio with the addition of simply a high pass filter.
Before you even play the audio you can see on Soundcloud’s crudely rendered wave form the ‘silence’ is quieter than on the non-HPF version. Can you hear how much cleaner the reading sounds?
Time for you to find out where your HPF is.
If you need more information about any of this please get in touch.