Tuesday, 12 January 2016

Transients versus bass, a common misconception

If you've ever had any form of audio engineering training, you will have almost certainly have come across the perceived wisdom that bass sounds take up the largest room in the mix. You will have been told to cut any sounds with presence below a certain point, unless they are bass instruments. You will likely then have gone home and tried this and wondered why your mix suddenly sounds like it has no life and no body to it and isn't really that much easier to master or mix. The truth is that bass is not always the culprit for db headroom. The largest eater of headroom is often transients.

Loud sounds often have a very pronounced spike in their soundwave, usually right at the start of the sound. This is called a transient. This can often be very loud in comparison to the nature of the rest of the sound, leading to it spiking out meters and limiters, while the rest of the mix is nowhere near that volume. So why aren't these just picked off by the limiter? The problem lies in the fact that all the parts of a mix intermingle at the same time and within the same frequency space. Limiting that snare drum's transient might end up taking down that hi hat with it if you just slap a limiter across the mix. Some win can be had from using a multiband limiter and isolating the frequency of the transient in question but i've found this to be a mixed results endeavour. Personally I find it more effective to limit or compress the part in question, prior to the final mixdown.

So how does this relate to bass? Well the nature of transients is that they are usually quite fast, hence the name transient, and as such are less likely to be made up of bass content. Bass takes time to develop (in the context of millisecond measurements) and is therefore not normally the cause of the problem. Bass instruments turned up abnormally loud can also cause issues with headroom, as the whole sound then becomes louder than other peaks, but generally speaking they are just more likely to muddy the mix and make the low end less defined.

The way I often go about detecting this transient issue is to slowly build up my mix, hitting it off a limiter with a readout of the gain reduction, and see what instruments lead to audible and visible dips in the meter. The most common culprit for me is the snare drum. That initial 'whack' of the snare can generate a transient that is so obnoxiously high above the rest of the music, it makes it impossible to master without ducking everything else at that point. The trick is not to even attempt to hit the whole mix with a compressor/limiter until we'v dealt with that snare separately, as discussed above.

So in conclusion i'm all for cutting bass in instruments if they are causing a build up or an unfocussed, muddy, low end. If, however, you just want to give yourself more headroom and more volume in mastering, i'd look to transients on individual instruments.

If you would like to see a worked example, I've done a video on it which you can see below

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