SSL Duende Tutorial 6 – Advanced EQ

Tutorial 6: Advanced EQ

Note to Pro Tools LE and M-Powered users:

Please set the H/W Buffer Size to 512 Samples. This setting can be found in setup>playback engine.

We all know the situation when you work for an hour on a particular sound, only to find when you take your mixer out of solo you can hardly hear the fruits of your labour against the rest of the mix.
This is generally down to the fact that there is not ‘space’ for that musical element within the mix. Other elements are present which occupy similar frequencies, therefore clash with each other. This is one factor which can often differentiate a professional mix from a demo.
The most obvious way to create space is to put all the elements at a sensible volume and pan settings so they stay out of each others way. Reverbs and careful use of dynamics are tools which can also contribute to placing an element in it’s own space, but EQ is often the first port of call when trying to achieve this. The more complex the mix, the more parts are fighting for room. This means that giving each part it’s own space is more important than ever and may take a while to achieve. If a song has just an acoustic guitar and vocal then finding space for them should not be an issue, where as a song using 100 tracks of audio would generally require a fair bit of ‘space management’.

Take for instance a recording of a hi-hat captured whilst the whole kit is being played. We are generally only interested in the higher frequencies present in the hi-hat track as the rest of the spectrum is other drums and unmusical content.
In this case it is worth employing the high-pass filter on the Duende channel to remove frequencies below 500Hz as we are not interested in these. Also when drums are close mic’ed there is usually more low frequency content present than would normally be heard if you were to listen to the kit in the room. This is due to the proximity effect which occurs when a microphone is placed close to the source, and can be compensated for by either filtering or rolling off the low end.

It is also worth bearing in mind that bass frequencies take up far more energy than high frequencies for the same perceived volume. So cutting low frequency energy out of signals which are only interesting in the highs can be a good practice, as it essentially means your mix can be clearer and louder because there is less low frequency energy present that takes up valuable headroom. But be careful not to just do this as a habit, and make an informed judgment about where the filter should be set based on what energy is present and what is wanted in the low end.

The same can be said for using the low-pass filter on sounds like bass instruments which are predominantly low in frequency. This is not so important from an energy point of view as this high frequency information contains comparatively little energy, but can help to clear up the top end of your mix.

Using the high and low pass filters in this manner is a quick an easy way to create some space in your mix. This can also be done by using the channel Eq high and low bands for a less heavy handed approach. Using the high and low band EQs in shelf mode means that the frequencies are getting attenuated rather that cut out all together. This can provide a more subtle result yet still prove effective.

Using the Eq section of the channel to control the middle elements of a mix (where the music is!) can be much more involved yet once it is done well can produce great results.

Using EQ to create space in a mix

Load the Tutorial 6 session.

Play the track and the notice how some of the parts are getting on top of each other. Try soloing different tracks together and notice the interaction between them. For instance, the rhy gtr 1, rhy gtr 2 and bass tracks have very little definition when played together. The drums sound slightly muffled as there are some middle and bottom end issues that need clearing up. Lets start with the drums and bass as they are the foundation for a track like this.


Solo the kick channel and open the corresponding Duende channel. Now bring the bass track into the soloed mix so we can get these two parts working together so they complement each other.
Press the BYPASS ALL button on the kick track to bring the processing into place with the bass still soloed.

  • The high-pass filter has been set to about 50Hz to let the bass breathe, and a boost of 5db has been added at 130Hz to compensate. This has been done to enable the kick to sit slightly above the bass.
  • A boost of 5db is used at 4kHz to emphasise the click of the kick drum. This is where most of the attack information is and will allow the kick to come through the mix.

Now open the channel on the bass track and look at the EQ settings.

  • The low-pass filter at 3kHz clears up the top end slightly as this is mainly noise.
  • A boost at 72Hz is used to give the bass some more weight.
  • A cut at about 740Hz is used to move the bass slightly out of the way of the snare which can be demonstrated by bringing the snare track into solo.
  • Finally, a boost at 950Hz is used on the bass to give it a little more body.

Now the bottom end is sounding tighter, clear all solos and lets concentrate on the hihat. With the Duende channel bypassed you can hear low end information which is not really needed on a track like this.
By bringing the Duende channel into play, you can hear how this has been cleaned up. The low-pass filter is wound up to 300Hz to eliminate this low end, and a boost at 4.5kHz gives the hats more bite and presence.

Lets have a quick look at the snare before bringing in the rest of the kit mics. Bear in mind that a lot of the snare in the drum mix will come from the tom-oh and room mic tracks.

  • A resonance has been found at about 730Hz which has been reduced with a LMF cut in this area (more information on this below).
  • The bottom end has been removed with the high-pass filter and a slight amount of punch has been added at about 200Hz.
  • Finally a small amount of top end has been added to bring a little life back into the sound.

Solo the whole kit using the ‘kit bus’ sub-group. Notice there is a bus comp placed over this group, and by bringing this into circuit using the ‘COMP IN’ button you can hear the drums working together more sympathetically to each other . Bring the bass track into solo and you can hear the rhythm section working well together.

Guitars etc.

With the drums and bass in solo, bring the rhy gtr 1 track into the mix. Open the Duende channel and hit the BYPASS ALL button.

  • The low end has been trimmed off using the high-pass filter and the lower-mid boosted.
  • The HMF band has been used to move the guitar out of the way of some of the drums and a top end boost to open the sound up without it sounding harsh.

Now bring the rhy gtr 2 track into the mix. With the Duende channel bypassed this track tends to bleed over the bass and rhy gtr 1. Hit the BYPASS ALL button to turn on the channel and look at what has been done to sit this in the mix better.

  • Again the low-end has been removed with the high-pass filter and the frequencies around the snare have been toned down.
  • A high-mid boost pokes the guitar through the mix and some high end opens it up slightly.
  • Some compression is used to even out the dynamics slightly.

Finally the pad has been sat at a low level and probably doesn’t need any EQ.

Now A/B the processed and un-processed mixes using the bounces at the bottom of the screen. With the Duende channels switched on the mix sounds more open and energetic with more definition between instruments. This is because each one has been moved into their own place within the mix.
Notice that the peak level on the master fader is in fact lower with the processed mix, but the mix sounds louder and bigger.

As in tutorial 3 these EQs were arrived at by processing ‘in place’, that is not in solo. For these purposes however we are soloing to highlight the different processing taking place.

Let’s go Hunting

Sometimes you will be presented with signals which exhibit resonances. These resonances are high levels of energy at a particular point in the frequency spectrum which are often not related to the music.
They tend to mask other frequencies and are generally not pleasing to the ear, and can become very annoying after a while. Vocals tend to exhibit these, as do instruments recorded with poor microphone placement.
A well trained ear will be able to hear, pin-point and pull out these frequencies without too much of a problem. However if you don’t know you’re frequencies off by heart there’s a tried and tested method for dealing with these gremlins. If you suspect a signal has a resonance which you don’t want to hear in your mix, here’s what you can do to control it.

Look at the vocal track in the tutorial file. Even though the vocal sounds fine on first listen, there are in fact resonances present which when controlled will enable the vocal to sit better in the mix and generally sound ‘flatter’. By flatter we mean that the frequency spectrum is leveled out, so there are no obvious peaks across the range. This can easily be seen on a spectrum analyser.

By using a high Q value and applying a large amount of gain, it has been found that resonances are present at 247Hz and 2235Hz. If you increase the Q values on the LMF and HMF bands to 2.5 and wind the gain up to about +15db, you can hear an exaggeration in the signal at these points. Now reduce the gain down to -8 db or so and decrease the Q to about 2. You will notice that the vocal sounds more open and intelligible.

Obviously how much cut you use to pull out the frequency is subjective, and beware that using large amounts of cut with high Q values can sound quite strange. This is why it is advisable to back off the gain and Q value once the resonance is found.