Two microphone preamplifiers compared at Abbey Road Studio 2 - tube and transistor
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In the recent test of three microphones on female vocals, one reader commented, "Do you need a reason why it's clipping? Bad engineer!"
Of course there is no such thing as a bad engineer, only a human being who perpetrated a single case of bad engineering. Of course if he or she continues to do so...
But I digress. As part of the test I intentionally included a technical fault, to see if readers could spot it. Actually it wasn't intentional, it was a case of bad engineering.
Even so, it wasn't so bad that anyone spotted it. In fact no-one spotted the single most serious fault in the series of recordings. No-one.
I'll come back to that in a moment, and there could be a reason for this surprising lack of perception.
What many people did pick on as the technical fault was clipping on the recording of the tube mic. Yes, it does seem from the waveform that the recording might be clipped, and it does sound a little edgy in these moments.
But there is no clipping outside of the microphone. The preamp gain was set appropriately for the Pro Tools HD interface. The preamp is easily capable of providing sufficient signal level, and there were no red lights, anywhere. Neither of the other mics displayed such apparent clipping, so I am very confident that the recording was made correctly.
Indeed, what you are hearing is the inherent sound of a tube microphone. Like it or loathe it, that is what a tube microphone sounds like. Actually, I like it.
The question also arises whether it is a genuine case of clipping. Tube amplifiers don't really clip, they just get more distorted at higher levels. That's what we sometimes call 'warmth'. It's a very subjective thing.
There is one point in the recording that sounds like clipping, at around 29 seconds. That's the singer - she had a cold!
There was one technical anomaly in the test. Due of course to bad engineering, well actually bad technicianing, the recording of Mic 3 is inverted with respect to the other two recordings, almost certainly due to the cable being incorrectly wired. It is a problem that occurs every now and then everywhere in sound engineering.
Phase inversion is normally tolerated. It is extremely difficult to tell whether a signal is inverted or not, and in any case loudspeakers mess up the phase so much at the crossover frequencies that the whole thing is pretty much a lost cause.
But there are situations where phase is important - recording in stereo with two mics is one, making comparative tests is another.
So here is the recording of Mic 3 again, firstly in the correct phase, secondly inverted (right-click, save target as)...
Now, the real fault. Listen to Mic 3 at the very end, during the final word. What do you hear? Now that I have pointed it out I am sure you will hear a slight click. Slight it may be, but this is outside of the bounds of professional quality.
Mixed in with other instruments, the click might not be audible, in which case it would be OK. Multitrack recordings of real instruments and vocals are commonly filled with all sorts of muck and crud, but in the context of the mix it isn't audible. However, if the click were as exposed as this, corrective action would be necessary.
Where did this click come from? That's a good question, and the answer is that I don't know. It isn't present on the other tracks, so it wasn't an acoustic sound. It could have been the singer's foot connecting with the leg of the mic stand. However, that normally results in a more bassy 'thump'. I'll have to leave it as a mystery until it occurs again and I can track it down.
So why didn't anyone spot it? Well I suspect that many people did, but they thought it was just one of those things that occasionally happens when you download files from the Internet. Unfortunately the use of computers and digital processing has conditioned us to expect clicks. And so in expecting them, we have come to accept them, which is sad.
Still, if you make sure that your finished mix or master is click-free, then you have done all you can and the rest is up to fate.