Mastering EQ, Tone and the Frequency Spectrum Tutorial
As I’ve mentioned, mastering EQ is possibly the most important tool you are ever likely to use. It is also one of the hardest to grasp. Even the slightest adjustments can have a detrimental impact on the whole mix. The skill of detecting what is required using mastering EQ will come as you practice the techniques found in this mastering tutorial.
EQ in mastering has more than one use. Generally it is used to bring tonal balance to a mix, although it can surgically correct problem frequencies like resonance. It can also play a musical role by exposing a hidden gem in a mix like the lush high mid of a synth pad, or the meaty low mid of a lead guitar. The trick is to know what you are looking for.
In most cases the fullest, or richest sounding music tends to have an even spread across most of the frequency range. This is very typical of pop music. In fact, the actual frequency curve for commercial pop, when viewed on a spectrograph, can appear to take the shape of a bell curve.
Have a look at the following two images, one shows peaks and one shows RMS.
Peak and RMS are explained further in the Dynamics Processing chapters, for now let me just say that peak is the highest level that the audio wave reaches, and RMS is an average of the peaks. The RMS level is closely proportional to the ears’ perception of loudness. On the Level metres to the right of each spectrograph, the dark blue indicates peak levels and the light blue indicates RMS levels.
Have a look at the following two images, one shows peak and one shows RMS. These are two snap shots taken from my spectrograph when playing a typical commercial pop song in Logic.
Side note: Peak and RMS are explained further in the Dynamics Processing (mastering compressor) chapters, for now let me just say that peak is the highest level that the audio wave reaches, and RMS is an average of the various levels making up the waveforms. The RMS level is closely proportional to the ear’s perception of loudness. For this reason you will probably find yourself monitoring RMS levels more closely than you will peak levels. On the Level meters to the right of each analyser plugin, the dark shade indicates the current peak level and the light shade indicates the current RMS level.
It’s a good idea to have a spectrograph (or a ‘multi-metre’ as the one I am using is called) inserted after all other processing as an aid to help you with what you are listening for. Voxengo offer a fantastic one for free known as ‘Span’.
Find it on Voxengo’s website.
Can you see what is meant by the bell curve?
When a mix has a rather low amount of mid-range frequencies compared to the highs and lows, it can sound thin, flat or hollow to the ear. On the spectrograph it may actually look as though there is a big hole in the mix.
Mastering EQ can help, to an extent. You can plug the hole with a gentle EQ lift in the specified area with a medium to low Q setting, producing a nice, smooth curve. Boost too far and the mix will sound un-natural.
Side note: EQ in audio mastering must be used with great care. Large adjustments can sound harsh and damaging, especially when boosting an area of frequencies. Did you know that hearing a reduction with EQ can be somewhat more pleasing to the ear than hearing a boost? If you want to hear an increase in one group of frequencies, it can sometimes be more effective to reduce the frequencies around it. It’s like a balancing act. If you reduce the lows, the mix can sound like you have turned up the mids and highs, reduce just the highs and the mix can appear to have more mid and low end. When using standard EQ plugins, it’s good to try and stick to using reductions if you can as they perform a reduction more easily, thus preserving sonic quality. The higher the quality of the EQ, the better it will be at performing a boost.
The job of creating this even spread of frequencies that the human brain is so fond of is, in all fairness, largely down to the mixing engineer. The audio mastering process should be seen as more of a time to fine tweak an already good balance of frequencies.
If, after looking at the two spectrographs again, I were to ask you to guess where the sonic energy was greatest, the low, the mid or the high frequencies, what would your answer be?
I think it’s pretty obvious that the most is happening in the mids. This has a great advantage when it comes to being played on a typical hi-fi or kitchen radio and here’s why…
The frequency response of the consumer’s music player is a big factor. Your finished master needs to still sound full and exciting when it is squeezed through a cheap kitchen radio’s frequency response of about 100Hz to 14kHz. For this to happen, the mids need to sound clear and defined with plenty of energy. A big hole in the midrange of a mix will be a lot more damaging when played on such a system as it’s mostly midrange that the speaker can reproduce. Let’s be honest, the consumer is not likely to have a set of studio quality monitors set up in their kitchen to listen to whilst they are cooking.
A small kitchen radio will struggle to produce low frequencies.
The extreme highs will struggle too.
This leaves mostly midrange to get your point across. An even bigger challenge are laptop and smart phone speakers – these struggle with the low mids too.
Side note: Getting clear and defined mids must be accomplished during the mixing stages. Mixing is another subject altogether but this really needs to be said. A commercial sound is only partly down to the mastering stages, the rest is down to the skills of the recording and mixing engineers. In the advanced audio mastering section (The Secret Notebook of a Mastering Engineer) there is a dedicated chapter on mixing with mastering in mind.
We all love to hear a powerful bass-line and a sparkly top end but it’s the mids that have the biggest responsibility. Have a look at the following three diagrams illustrating how an even curve, and an un-even curve translates to a set of studio quality monitors compared with a small kitchen radio…
Side note: I have exaggerated the two illustrations with low midrange content to help portray my point. The spectrograph is only an aid to what you are hearing. It cannot be relied upon as a way to make decisions. Sometimes what you are hearing will not appear as what you may expect on the spectrograph.
I hope that you can now see how the tonal balance should not just be a matter of taste, but also a step towards equipping the track with the elements required to sound great on a wide variety of audio systems.
Next Page… Linear Phase EQ Parameters