Undisclosed Bass

I’m reviewing a shiny new Denon home theatre receiver that, amongst other things, features the ability to play Internet radio. Making sure I cover everything, I explore its menus and confirm that it also plays podcasts. To test, I usually go to the Skeptics Guide to the Universe podcast. Not a problem, there it is under the Science genre within the Podcasts section. To double check, I start playing it back.

Now this is episode number 272 — the most recent one as I write — and I have listened to every one of them. The last 250 or so have opened with a musical theme, followed by a woman with an English accent saying: ‘You’re listing to the skeptic’s guide to the universe, your escape to reality.’

But this time it is different. Why would that be? Something is going on only as she is talking, between about four seconds and ten seconds into the podcast. Why, in this area right here:

What you can see there is the waveform for the first 19 seconds of this episode of SGU, low pass filtered at 20 hertz. As you can see, there is virtually no infra-20 hertz content in this, except for that section, where there is masses of it. How much? Look here at this frequency spectrum showing the bottom few octaves of that six second segment:

That peak is at 11.5 hertz, and the shoulder to its right is at 14 hertz. The flattening out after the descent is achieved at about 17 hertz.

And that’s what I felt. During those few seconds, there were palpable low frequency compressions of air in the room. Somewhat audible, which I put down to the harmonic distortion components being up in the audible band. But most of the energy would be, by my guess, at the originally recorded frequencies. And look at that energy: it’s a full 18dB above the average energy level in the 40 to 1,000 hertz band!

This was a total surprise. I pulled up the podcast for episode 213 and played it, with the same problem. It has likely always been there, and I have likely failed to notice it some 250 previous times. So why now?

Why now is the Paradigm Sub2 I am testing, with its six ten inch drivers and its claimed 7 (seven) hertz at -3dB.

I have previously pointed out that sometimes unintended bass noise makes its way onto recordings due to the inability of the monitoring equipment to reproduce it. This subwoofer threatens to reveal a whole new category of unintended noise on recordings.

It has been a while since I’ve given anything away, so how about the Blu-ray of The Lord of the Rings: The Fellowship of the Ring. Details on the disc here, including Blu-ray vs DVD comparison. No proper box, and no proper disk label, but the data content of the disc is identical to a bought one. Ask for it in comments. Australian addresses only (the disc is locked to Region B).

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