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The problem is that we have unrealistic expectations of what drums should sound like on a recording. Listen to a good drummer, live with no amplification. Does it sound anything like what you hear on record? Distinctly, no.
The sound we like from recorded drums is a hyped-up, ultra-clear version that could only be heard for real by a space alien with eight or more prehensile ears. No wonder it is so difficult to achieve.
To capture drums in ultra-clarity, each drum has to be close miked. This means that we need one mic for each drum, one for the hihat, and then two overheads to pick up the cymbals and the general sound of the set.
The problem is though that each mic (other than the overheads) doesn't pick up only its assigned drum - it picks up the rest of the set too, and pretty loud.
Solo a mic and you will hear this very clearly.
And all that spill from the other drums and cymbals is what is causing the 'mush' that you will struggle so hard to get rid of.
Of course, the first defense against mush is to take great care over the positioning of the mics. The next step that many engineers take is to use noise gates on all of the individual mics. This totally silences each mic other than when its assigned drum is played.
This works to an extent. But there are some problems...
Firstly, it is very difficult to set the threshold of the gate so that it reliably opens when a drum is hit, and is reliably closed when there is so much noise all around the mic it is gating.
Secondly, the 'on and offness' of a gate is extreme. Any problems can be clearly heard. Gates generally have a control to reduce the amount of attenuation provided when closed, but it is still an 'either/or' situation.
Expanders can be better. Expanders too have a threshold, but they gradually increase attenuation below the threshold, rather than switching suddenly.
But there is a unit that is even better than an expander. And you won't believe what it is...
A Dolby A noise reduction unit in playback mode.
Dolby A is a noise reduction system that was designed back in the 1960s to reduce the hiss from analog tape. It prospered right up to the point where digital multitrack was a viable alternative. From then on, the reason to use analog was because of its characteristic sound, so noise reduction was pointless. If you wanted freedom from noise, you used a digital multitrack recorder.
But if you could get your hands on a few Dolby A units now - models 360 and 361 are good - you will find that they are excellent for cleaning up drums.
Dolby A works by splitting the frequency range into four bands and processing each band independently. On playback, signals above -40 dB or so are left unaltered, signals below -40 dB are progressively lowered in level up to around 10 dB maximum.
In normal use, the reverse of that process would be used during recording. But engineers in the 1970s would commonly record the drums without Dolby A encoding but use Dolby on playback to get the multiband expansion it provides.
And because it splits the signal into four bands, it is better than a simple expander can ever be.
There is one drawback - Dolby A provides a double layer of processing at high frequencies, so the output in playback mode won't just be expanded, it will be over-expanded at high frequencies. But this is a small problem that can be dealt with using a little EQ.
Dolby A units can be bought secondhand for a tiny fraction of their original cost, and for drum recording they are worth their (significant) weight in gold.
Or perhaps someone right this minute is developing a Dolby A plug-in...