What frequency range is considered to be ‘Low End’?
Why is mixing bass so difficult?
Who are you mixing for?
Source Audio
MIXING THE KICK
Getting your kick sound
Tuning
A kick that has no relation to the key of a track can work well if it has the right attitude and characteristics. However, a kick that is tuned with the key of the track will on most occasions groove with the music and sit better in the mix. Find the root note of your track and match the key of the kick to this note. To identify the key of a kick you can use an EQ with a frequency analyser and sweep the low end to find where the note resonates. You can use Logic EXS24 to change the key of your kick if you need to. Convert your kick sample to ‘New Sampler Track’ then transpose the pitch to the desired key. Your low end may just magically fall into place.
Its difficult for the human ear to identify the tuning of frequencies this low. Use this chart along with a frequency analyser to help you find the root note of your kick.
Pressure Point
The pressure point is the frequency range in which the kick packs its punch. The ‘woomf’ that hits you in the chest. Use this chart to help you find the pressure point.
Root vs 5th
Tail Length
This often overlooked aspect of the kick is of paramount importance when it comes to mixing low frequencies. Slight adjustments in the length of the kick tail can make or break a mix.
Controlling the Tail
An effective way to adjust the kick tail is by using fades on each sample. Below you can see examples of three different types of fade, all of which have a different effect. Fade A is a normal fade and will bring down the level of your kick tail smoothly. Fade B is a quick fade. This will have a very obvious tail shortening effect on your kick. Fade B works very well when you have other prominent bass parts in your track. Fade C is a more subtle approach. Use this curved fade when the kick is a driving and dominant aspect of your track, but you feel it could be tamed.
Avoiding Clicks
If you decide to shorten the length of your kick, be sure to add a fade out. This will prevent a small click at the end of your sample that will happen due to the cut audio wave.
MIXING THE BASS
The genre and vibe of your track will be factors to consider when choosing your bass sounds. Much like the kick, its better to have a full and deep sounding bass that you can cut and sculpt to your taste. If your original bass sound has weak low end energy, a low end EQ boost will only get you so far.
Kick vs Bass dominance
The low end spectrum only covers about 250Hz. This is a small amount of physical space compared to mid and high frequencies that have a range of thousands of hertz. Overlapping low frequencies make a track sound muddy and use up valuable headroom. For that reason, it is important to choose which element is more important to your music, the kick or the bass. In most scenarios, one must give space to the other.
Kick dominance
For the kick to stand out, the low frequencies in the bass need to ‘duck’ out of the way of the kick. This is done using side chaining. If you have a bass synth that has a lot of detail in the mid and high frequencies then you may only want to reduce the conflicting frequencies. Below you can see how I’ve used a multi-band compressor to select only the lowest bass note to duck it out of the way of the kick.
Bass dominance
You may want to have the bass dominating over the kick. How you do this will depend on your source material. If you have long bass notes you may want to reduce the tail length of your kick. This will free up that space for your long bass notes. Alternatively, If your bass is playing short stabbing notes you may want to control the attack of the kick. By reducing the attack of the kick we give space to the bite of a punchy bass. We can achieve both of these characteristics by compressing the kick in different ways.
Similarly to adding a fade as discussed earlier you can compress a kick to lower the level of the tail. This will give your long bass notes space to be the prominent feature in your mix.
Reducing the attack of the kick is best achieved using either a compressor or a transient shaping plugin (such as SPL Transient Designer) you can copy the settings I have dialled in below and tweak to your taste.
Clearing The Mud
The 'mud' in a mix is when there is a lack of clarity in the sounds. It's a frustrating problem that many producers come across. It's actually very easy to clean up the mud during the mix stage. The lack of clarity is generated when more than one audio source is trying to occupy a certain frequency range. This can be more obvious around 100-350Hz. One way to reduce the mud is by identifying audio tracks that are emitting bass information when they shouldn't be. For example, when recording a live audio source with a microphone, such as guitars and vocals, unwanted low frequencies can creep into the mix. You can use a high pass filter on an EQ to cut these low frequencies out without affecting the audio you want to keep.
Bass Space
Your bass and kick have a lot of low end energy. To reach their full sonic potential in the mix, they shouldn't be competing for space. I created a dedicated section in my plugin LEVELS to analyse when there are too many competing low frequencies in a mix. 
1. Identify which instruments are your main bass sounds. (kick, synth bass, bass guitar, bass pad, sub drop etc)
2. Mute all of the important bass sounds you have identified.
3. Open LEVELS on your output channel and select ‘Bass Space’. The meters will go into the red when the low frequencies are too over powering.
If you find that there is still a lot of low end energy in your mix, you should find the guilty channel or channels and place a high pass filter to remove the unwanted low frequencies. This will free up space for your main bass elements and give you a cleaner mix.
CLICK HERE TO LEARN MORE ABOUT LEVELS
MONO
Placing your low frequencies centrally in your mix will give you a solid and powerful sound. The Kick and bass carry a lot of energy. If they are panned even slightly left or right it will give your mix a lopsided feel. This will also result in poor mono compatibility. The track will sound totally different when played through a club sound system or in other scenarios using mono.
LEVELS - Stereo Field
LEVELS has a great tool to look at the stereo placement of your low frequencies. In the Stereo Field section there is a ‘Low Pass’ button which solos everything below 300Hz. Above you can see the visualiser is showing wide low frequencies in red. It has also triggered the threshold which has turned the section navigation red too.
Here we see the issue has been rectified. The low frequencies are now placed centrally in the stereo field. Pure mono would show a thin vertical line. I would recommend having your kick in pure mono. But its not detrimental to have a small amount of width on your bass. Just don’t take those low frequencies too wide.
CLICK HERE TO LEARN MORE ABOUT LEVELS
EFFECTS
Distortion and modulating effects (flange/phaser) can shape your bass and make it sound really interesting. These effects can also make your bass more audible in the mix. Reverb and delay can also sound great on both your kick and bass. However, these effects can reduce the clarity of your mix if used carelessly. Parallel processing is a great way to introduce these effects to your mix without negatively affecting your low end. Below is an example of how you can add a reverb to your bass part.
Create a send to an auxiliary channel. On your new aux channel insert a reverb plugin, set it to 100% wet and create the sound you want. Place an EQ after your reverb plugin and use a high pass filter to remove the low end information up to around 250-500Hz (use your ears, select whatever feels good). Then use the volume control to select how much reverb you want. With bass reverbs it's best to keep them quite short to minimise the masking effect a reverb can have. Having a short pre-delay can also help separate the reverb from the source material which will improve clarity.
Without the EQ removing the bass from the reverb, phase issues are introduced into the mix. This is proved by the red dots on the vectorscope on the left. When the EQ is engaged the phase issues are removed as proven by the vectorscope on the right.
HARMONICS
Harmonics are an important characteristic when it comes to the perceived loudness of low frequencies. If the fundamental notes in the bass are happening around 60Hz or below we will be able to better interpret the sound from the first harmonic an octave higher. Interestingly, our brains are able to 'imagine' very low fundamental frequencies if we can hear the harmonics. This is true whether the fundamental note is present or not. It is also important to note that not everybody will listen to your music through full range speaker systems. A lot of music is consumed through laptop speakers with a poor low end response. A harmonic exciter will help make your bass more audible on these systems.
Load up a harmonic exciter, saturation or distortion plugin onto your bass. Try and monitor through small range speakers whilst selecting the amount of harmonic excitement you want. Then move back to full range speakers and tweak to your taste. A harmonic exciter may reduce the perceived and actual level of the fundamental frequencies. If your music will be played through a full range club sound system be careful that you don't remove too much of the fundamental information.
ACOUSTICS & MONITORING
To make good mix decisions, you have to be able to hear exactly what is happening. This is particularly difficult when it comes to low end for a number of reasons. Firstly, accurate full range speaker systems are expensive. And secondly, without acoustic treatment even the most expensive speakers are ineffective.
The shape and size of a room, along with the density of the walls will have a unique effect on sound heard within the space. In a nutshell, sound generated through a monitoring system will jump around a room in such a way that it sound sounds very different when it reaches the listeners ears. The acoustics in a room can create peaks and dips of up to 35dB giving the listener a very false representation of the sound. To control the low frequencies in a room, thick bass traps should be be placed along any 90 degree angles in the room. You can't over do bass trapping so install as much as you can.
Full range speakers in a treated studio environment will give you an accurate representation of your low end. This, however, isn't always available. If you understand the limitations of your room acoustics and gear then you can compensate and point your mix in the right direction. As stated earlier, a small kitchen radio for less than $50 can be a great tool when monitoring. If you can make your mix sound great through that, it will sound even better when played through other systems. I also advise you to listen at a very low volume. This will minimise the rooms affect on the audio, reduce ear fatigue and help you get a natural balance of the instruments in your mix. .
SubWoofers
Subwoofers can extend the frequency range and give the listener greater insight into what's happening in the low end. However, more often than not they cause more problems than they solve due to incorrect installation. It also worth noting that the cheaper subwoofers will simply produce an inaccurate, mono tonal 'woomf' sound. Again these do more harm than good as you're not hearing what's truly happening in the mix.
When placing a subwoofer in a room, avoid the corners and any positions that are equidistant from two adjacent walls. This will minimise the negative effect of standing waves. When you hook your subwoofer up to your satellite monitors, try and have the crossover at around 80hz. The crossover from subwoofer to satellite speakers is the crucial make or break moment for a sub setup. The last thing you want is a 'hole' at the crossover point.
Even though it might sound impressive to have the sub at a high volume, if you frequently monitor at this level you will end up with bass light mixes. Follow the instalment instructions and manufacturers recommendations to get an even and flat bass response. 79-85 dB is a good level to monitor at when making adjustments to bass. More than 85 dB and the bass will feel louder, so you will bring the low end down in the mix which leads to a bass light mix. Quieter than 79dB and the low end will feel too soft which will lead to you boosting the bass too much. Keep this in mind when monitoring at different levels.
