Most people in music understand that in order to increase or remove a particular/set of frequencies you would use an EQ. Which is correct BUT saturation is often an overlooked alternative to EQ.
An EQ is a tool best used for increasing or decreasing the amplitude (in dB) of a chosen frequency band. They come in both hardware units and software plug-ins and can be used from the production stage, though to mixing and ending up with mastering. Nothing new there.
Saturation is a tool used for increasing harmonic content, typically odd harmonics when using tape or an emulation plug-in of a tape machine. This happens by simply clipping the audio signal - and there are many different ways to clip an audio signal. Each different clipping type will give you a different response in even/odd harmonics, the amount of compression that is induced and the overall tone etc. Think about guitar distortion, O/D and fuzz pedals, they all clip a signal... but they all sound different. And the more you use the less dynamic the wave-form is.
One thing to clear up here would be the difference between saturation and distortion. For those that use Pro Tools there is an AVID plugin called ''Lo-Fi'' and you have the ability to change the two parameters. Simply put - Saturation is a more subtle increase in harmonic content and Distortion is the extreme end of saturation. The effects are different and they can be used in different ways, as an alternative to EQ. So what are the differences and how can they be used?
I personally love saturation and I love to use it as a surgical tool more so than a creative tool. Not all of the time but most of the time. Saturation tends to make things sound BIGGER and you can target specific frequency ranges rather than exciting the entire signal. If the entire signal is effected it can decrease the amount of high end information and can be a unique alternative to a LPF. Distortion has a much 'grainier' and apparent effect and can increase top end information often making the signal sound 'spitty' and aggressive.
Here's some useful ways to use both;
1) Saturation on Kicks and Snare - Target the fundamental areas on both the kick and snare on their given buses (when summing multiple channels together). This will let the 'note' of each stand out a little more also making them sound a little thicker. OR use it on an individual channel and enhance what it is offering to the mix. For example; Saturating the bottom snare mic' only to get a more aggressive bite. Push it up in the mix and use the snare bottom channel as an EQ, making the overall snare sound brighter and slightly more aggressive.
2) Taming over-heads or hi-hats - If you have been given a song to mix which has an unbearable amount of high frequency content (typically on the OH's or HH's) using saturation can often be better than using an EQ. AVID's ''Lo-Fi'' plugin does this great. If you slowly increase the amount of saturation you will hear the high end frequencies reduce and the low end content will increase which, when set correctly, will give you a well balanced track to use in a mix. But you will have to be very subtle, I typically don't need to go above 0.2-0.5% when using the ''Lo-Fi'' plugin.
3) Making bass-lines phat again - Bass content has a habit of fluctuating in volume depending on where the fundamental resonance lies. The most obvious loss is heard when using sub-bass on EDM or similar music. Saturation can help even the response out AND give the note more definition. I also suggest that you automate the fader level to compensate for the remaining loss.
4) Making an instrument group sound huge! - When using a bus to group your instruments together try increasing the harmonic content of the entire group being summed together! It'll increase the ''glued'' together sound and make things sound big & fat. Try it on vocal groups, FX groups, the lot!
Here are some saturation plug-ins that I use;
1) Sound Toys - Decapitator
2) Sound Toys - DevilLoc
3) Slate - VTM
4) Waves - J37
5) Waves - MannyM Distortion
6) JST - Clip
7) Avid - LOFI
8) FabFilter - Saturn
9) Audified - STA Pre-amp
10) Nomad - Pulsetech
Give it a go, the worst that can happen is that you simply do not like it. After all, this is the job where everything is based on personal taste! But when you're dealing with awkward bands where ''eVeRyThInG hAs tO sOuNd BiGgG'' it can be a great way to get just that without ruining your mix! Alex