| Although it's possible to create a decent mix without | | | | quarter (25%). Thus, only 25% of the original sound |
| any filters at all, they are sometimes very useful. In | | | | remains and it will be damped with 75% at 1000 Hz. |
| addition they can be used to change the fundamental | | | | But let's say you used a mixer which has a 4th order |
| character of a sound, rather than just boosting or | | | | low-pass filter and you filtered it the same way as |
| cutting certain regions to make small adjustments. But | | | | above, at 2000 Hz. Then the slope of the curve would |
| how do filters really work? | | | | look "more vertical" because it would cut more |
| Most mixers are equipped with a filter section which | | | | efficiently. |
| has a bass, mid and high frequency region that you | | | | A 4th order low-pass filter looks almost the same as |
| may boost or cut. In many cases there's one knob for | | | | a 2nd order one, but not exactly the same. The slope |
| the bass, one for the high frequencies (treble) and one | | | | cuts even when you move to the left (down in |
| or two knobs for the middle region(s). | | | | frequencies). |
| If the filters have one knob for the bass, one for the | | | | So if you tweak the 4th order low-pass filter knob and |
| treble and two knobs for the mid range then you | | | | set it to 2000 Hz, as with the 2nd order filter, then it'll |
| cannot choose exactly which bass frequencies that | | | | cut more of the frequencies below 2000 Hz than the |
| should be boosted or attenuated, nor which treble | | | | 2nd order filter did. Frequencies around 1000 Hz will still |
| frequencies these knobs should boost or damp. | | | | be heard, but as you can see they are almost silent as |
| Instead the bass knob works as a low-pass filter | | | | compared to the 2nd order filter where they were |
| which cuts at a fixed frequency , for example 100 Hz, | | | | only reduced by 75%. |
| and then adds or subtracts the result to or from the | | | | In the 4th order case they will be reduced with 24 dB, |
| original sound. The treble knob works like a high-pass | | | | because we use a 4th order filter (4*6 = 24 dB) and |
| filter which cuts at a fixed frequency , for example | | | | one octave below 2000 Hz would be 1000 Hz. And |
| 10000 Hz, and then adds or subtracts the result to or | | | | since the filter damps 24 dB per octave then |
| from the original sound. The mid frequencies can | | | | frequencies at 1000 Hz will have the volume reduced |
| sometimes be adjusted both in terms of which | | | | with 93.75% (24 dB). |
| frequency band that should be boosted or attenuated | | | | So how did we get 93.75%? 6 dB is half (50%). 6 dB |
| and how much. Or they work on a fixed frequency | | | | again (total 12 dB) means 25%. Another 6 dB (total 18 |
| region, which is neither bass or treble, but somewhere | | | | dB) means 12.5%. And finally the last 6 dB (total 24 dB) |
| in between. | | | | means 6.25%. Thus, only 6.25% of the original sound |
| Pros usually need to sweep not only the mid range | | | | remains and it will be damped with 100 - 6.25 = 93.75% |
| frequency, but also the bass and treble frequencies. | | | | at 1000 Hz. |
| However, that doesn't necessarily mean your mixing | | | | With a 4th order low-pass filter which cuts at 2000 Hz |
| desk (or mixing software) must be equipped with such | | | | you will still be able to hear audio which is located |
| filters, to work like the pros. You can use external filter | | | | around 2500 Hz. It'll be damped, but it might still be |
| modules (or plug-ins), such as equalizers, to achieve the | | | | possible to hear it. On the other hand, with a 4th order |
| same result. | | | | low-pass filter you'll hear less of the audio at 2500 Hz. |
| What newbies often forget is that filters, such as the | | | | That's why it might be more difficult to create a good |
| bass and treble knobs adjust the volume. Yes, the | | | | mix with certain filters. In general I'd suggest that you |
| volume. The bass knob, for example, is used to decide | | | | use at least 3rd order (18 dB / octave) filters when |
| how many dB you should boost or cut in the bass | | | | you're mixing. If your mixing desk features only first or |
| region. Moving the knob to the left cuts a certain | | | | second order filters, then you might consider using |
| amount of dB. Moving it to the right boosts a number | | | | external filter modules or plug-ins as inserts. |
| of dB in the bass region. Thus it boosts or cuts the | | | | But there are a number of different filter types as well |
| volume in the bass region. | | | | and not only the order decides whether it'll be useful or |
| If you check the marks on the bass knob and move it | | | | not. Let's have a look at some filter types, which can |
| 6 dB to the right, then you will increase the volume on | | | | be used to solve mixing problems, rather than to |
| that track with 6 dB, but only in the bass region. | | | | change the sound itself. |
| Consequently, filter changes result in volume changes, | | | | There are a number of filters on the market and they |
| but only in certain frequency regions. | | | | complement the traditional, low-pass, band-pass and |
| Boosting the bass with 6 dB means that the volume | | | | high-pass filters which most mixers are usually |
| will increase although you didn't touch the volume slider. | | | | equipped with. You might consider using them as |
| Assume that you have decided to use an almost | | | | inserts to solve problems on certain tracks. |
| perfect a slap bass sound, but you want to adjust it. | | | | The notch filter removes a certain frequency range |
| Then you might notice that you get almost the same | | | | (thus it creates a dip in the frequency spectrum). |
| effect by turning the filter's knob as you would by | | | | It's the opposite of the band-pass filter, which passes |
| turning the mixing desk's volume slider. That's because | | | | through a certain frequency band. |
| the slap bass sound contains bass frequencies only | | | | So what can it be used for? Well if you don't own a |
| (well, almost). So if you're using filters to the change | | | | dedicated de-esser, then you may use a notch filter to |
| the color of the sound you might boost or cut a lot of | | | | remove regions in a vocal recording which cause |
| the volume on that track just by turning a filter knob. | | | | problems. And you may reduce or remove 50 Hz hum |
| The two knobs for the middle region allows you to | | | | caused by bad cables or just get rid of frequencies |
| choose the frequency (knob 1) and how much that | | | | which you don't like and which don't seem to work in |
| frequency region should be boosted or cut (knob 2). It's | | | | your mix. Bass, mid and treble filters let you attenuate |
| the same here with these knobs and with the treble | | | | certain bands, but their frequency range might be too |
| knob as with the bass knob. If you're using an | | | | big sometimes, when all you want to do is to reduce a |
| instrument on that track which has its frequency | | | | small region, such as 40-80 Hz. Then a notch filter |
| content concentrated to the mid region, then boosting | | | | might be useful. |
| and cutting the mid region will have almost the same | | | | A comb filter creates a metallic sound. It's frequency |
| effect as moving the volume slider on that track, so be | | | | response is quite interesting. Different implementations |
| careful. | | | | have different frequency responses, but in general it |
| A common mistake is to boost only. That is to tweak | | | | looks like a comb (or saw teeth) with dips and peaks. |
| the amount knob to the right all the time. But filters are | | | | That's why it's called a comb filter. |
| indeed used to remove frequencies as well. | | | | As you might understand, It's not the kind of filter which |
| Sometimes if you feel that you need to filter a sound, it | | | | you use in every mix and on lots of tracks, because it |
| can be useful to try cutting a couple of dB | | | | changes the sound quite a lot. |
| somewhere, rather than boosting. The snare drum is | | | | However, if you're working with a sound which is dull |
| such an example. Often it takes far too much space in | | | | and needs processing to become more exciting then it |
| the mix, because it contains a lot of high frequency | | | | can be worth a try to process it using a comb filter, |
| content, in its unfiltered state. Cutting the high | | | | possibly in combination with an effect, such as a |
| frequency content of the snare drum can make it "sit | | | | chorus or a flanger. |
| better" in the mix, blending in with, say, the vocals or | | | | One of the better ways to make a sound more living |
| other instruments. It becomes more subtle. | | | | and interesting is to process it through a formant (or |
| So when should you boost the filter and when should | | | | vowel) filter. Formats are regions in the frequency |
| you cut frequencies? Well, there are a couple of easy | | | | spectrum which are associated with different vowels. |
| answers. Microphone hum should of course be cut | | | | For example, the vowels a, e, i, o and u have a set |
| away using the bass filter. Some mixers even has a | | | | (around 5 or 6) of peaks and cuts in the frequency |
| low frequency filter, which is a button rather than a | | | | spectrum and they look different for each vowel. A |
| knob. It cuts say 12 or 24 dB between 0 and 50Hz, to | | | | formant filter lets you apply these boosts and cuts in |
| get rid of hum. | | | | the formant regions on your track. |
| But there are other situations when it's more difficult to | | | | A formant filter can make a dramatic change to the |
| judge whether you should boost an instrument in the | | | | sound, a much more dramatic change than using a |
| high region or cut another. One rule of thumb though is | | | | simple low-pass or high-pass filter. The formant filter |
| to balance the filtering almost the same way as you | | | | makes the audio sound more like the vowel which the |
| balance the panning. You cannot just boost all the | | | | formant filter emulates. |
| tracks in the high frequency regions. It's pointless. It's | | | | There are filters which adapt their frequency response |
| the differences which create the result. The problem is | | | | to a track and make it possible for you process your |
| often that two tracks are too similar and something | | | | track(s) using these settings. You could feed your |
| needs to be done about it. Thus boosting both of them | | | | favourite music through the filter. It checks the |
| won't make much of a difference, but cutting one of | | | | frequency response of the recording and then you |
| the tracks with say 3 dB and boosting the other in | | | | may apply that frequency response on your own |
| another frequency region with, say, 3 dB can make a | | | | recording. E.g. you can make sure that your track has |
| difference. | | | | almost the same general frequency response as |
| Boosting from 2000 Hz and upwards or cutting the | | | | some of your favourite commercial tracks. How does |
| lower frequencies of the sound, starting at 2000 Hz is | | | | it work? Well, assume that you know a recording |
| practically the same. The frequency responses are | | | | which sounds excellent. And you feed it through the |
| similar. The only difference is that the boost resulted in | | | | filter. The filter then analyses the recording and adapts |
| a higher overall volume. | | | | its frequency response. |
| Attenuating a region of sound and raising the volume | | | | The filter allows you to apply or impose the frequency |
| will have the same effect as boosting the region of | | | | response of the analysed track on your own |
| the sound which wan't attenuated. | | | | recording. |
| Almost all mixers have different filters and | | | | The filter adjusts the overall frequency response so |
| consequently they all sound different (mixers from the | | | | the higher region of your own recording sounds more |
| same manufacturer often have the same type of | | | | like the higher region on the original recording etc. |
| filters though). There are a few things which determine | | | | These type of filters can can actually transform your |
| how the filters sound and how good they are. One of | | | | recording from something which sounded like a |
| the most important characteristics of a filter is how | | | | relatively dull mix to a recording which has commercial |
| steep the slope is, or in other words how many | | | | qualities. |
| degrees the filter has. | | | | There are two types of schools when it comes to |
| Some manufacturers say their filters are 4th order | | | | mixing. Either filters are used to make very subtle |
| low-pass filters or 2nd order high-pass filters. 4th order | | | | changes to the sound, for example by cutting or |
| or 2nd order means that the filter cuts 24 dB per | | | | boosting with 1-2 dB in a region. The other school |
| octave or 12 dB per octave. So how did we get 24 | | | | makes use of extreme filter settings. Filters are applied |
| and 12? 4th order means 6 dB times 4 equals 24. | | | | to a high degree on each track, to make them sound |
| Each "order" means 6 dB. | | | | as different as possible, making it easier for you to |
| Thus each order of a filter means cutting (or boosting) | | | | blend them together in the final mix. |
| the volume in half (or boosting twice). In other words, | | | | Whichever method you choose is up to you. It also |
| the order of a filter is measured in terms of how much | | | | depends on which type of music you make. If you're |
| it cuts (or boosts) if you move an octave up or down | | | | into synths, mostly, then the synth sounds themselves |
| in the frequency spectrum. Confused? | | | | have been filtered to a high degree before they |
| A low-pass filter cuts off more and more of the high | | | | reached the mixing desk. Alternatively, the filters in the |
| frequencies as you move the knob anticlockwise | | | | mixer become part of the actual sound generation |
| (down in frequencies). So if you turn a low-pass filter | | | | rather than being tools to put the mix together. |
| knob and set it to, say, 2000 Hz, then the audio below | | | | Filters can be used to make tracks work together in a |
| 2000 Hz will be preserved. However, frequencies at | | | | mix. If two sounds are very similar and they are |
| 1000 Hz will still be heard. They won't be silent. But they | | | | competing for the same space in the frequency |
| will be reduced with 12 dB. Why 12 dB? Because we | | | | spectrum, then it can be a good idea to apply some |
| use a 2nd order filter (2*6 = 12 dB) and one octave | | | | filtering on one of the sounds, or both. |
| below 2000 Hz would be 1000 Hz. And since the filter | | | | Try boosting or damping a region like crazy on one of |
| damps 12 dB per octave then frequencies at 1000 Hz | | | | the two tracks, and try boosting or damping another |
| will have the volume reduced with 75% (12 dB). So | | | | region on the other track. Then their frequency |
| how did we get 75%? 6 dB is half. Yet another 6 dB | | | | spectrum's will be much more different then they used |
| (making 12 dB) cuts in half again and half of a half is a | | | | to be and the similarities will be reduced. |