Too Busy For Words - the PaulWay Blog

Fri 25th May, 2007

Hardware problems

I completely failed to record the CLUG meeting last Thursday night, basically because I just didn't think it through enough. I set out with good intentions, a nice stereo microphone, a five meter extension cable to allow me to monitor the recording without being up the speaker's nose, and a little impromptu microphone stand I'd fashioned out of some handy wood (the old 'if all you have is some wood' design criteria). I'd tested the set-up before and made sure the microphone was working, and got the levels right beforehand. I started recording way before the first speaker, so I could check that it was all working again.

The first minor glitch was discovering that I couldn't record and play back simultaneously. So I could watch the levels moving up and down, and note that they were at least vaguely reacting to the speaker and the audience, but I couldn't check that what was recorded was actually sensible. I tried stopping one recording (again, before the first speaker started) and then continuing recording in another session and playing back in the first session. Audacity played nothing. I tried to normalise the first while the second was recording. Audacity crashed. Don't do that again, then.

The first clue that something was going wrong was that the levels weren't following David's talking closely enough. They'd pick up loud noises in the room, but not David's pauses. The second clue was that this changed before Tridge started talking - the levels went up - but they stayed even flatter. Tridge knows when to raise his voice - we have no amplification for the CLUG meetings - and I should have seen definite peaks. And the levels weren't flat, either - so it wasn't recording silence. I thought I hadn't changed anything when the levels went up, but as it turned out I had.

The third clue had to wait until I got the recordings home: I listened to one and I could hear my comment to Tridge sitting beside me fairly clearly, but not his response. Otherwise, it was mostly buzz. Diagnosis: something was working, but the noise from the circuitry on the rather ordinary on-board audio was pretty high (no surprises there, laptops are not renowned for their onboard sownd, er, sound). And why had the levels gone up for the second recording? What had I changed? I couldn't remember. It took a sleep for it to all congeal in my head, and the next morning the ghastly truth of my elementary error flooded into my brain unbidden:

I had put the microphone in the headphone jack, and vice versa.

This is why it picked up vague noises, and could hear my comments: because headphones will act as fairly microphones in a pinch (it's just the same circuit, only being read from rather than written to, if you will). This explained why the noise had gone up but no voice had been actually recorded in the second phase: because I'd unplugged the headphones half-way through (since they were useless as monitors). From then on it was picking up uncompleted circuit noise. And what had probably done it was that the extension cord from the microphone looks a lot like the extension cord that I use at home to plug my audio output into my home-made switch board.

So: save up for a nice Edirol UA-1EX USB adapter which can do 24-bit 96KHz recording and playback and has a microphone input, and possibly a nicer microphone stand so I don't look quite like a reject from Woodworking 101 with it. And try to solve the hardware problems in my brain before doing this again.

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