You can’t test everything

In my reviews I try pretty hard to find all the defects in a product that could reduce user convenience or performance, but, of course, I frequently miss stuff.

Last night I was playing a CD of The Who’s Tommy, and things were very peculiar with the sound. The kick drum seemed to be quite out of time with the rest of the music, and there seemed to be a mid-bass lumpiness that shouldn’t have been there. I was using small Krix speakers and a Krix subwoofer, and in my experience Krix stuff is pretty good. So what could be going on?

I plugged in a pair of headphones and the bass kick seemed back in place, so it wasn’t something weird on the CD that I had previously failed to notice. Maybe, I thought, I had the distance setting on the subwoofer in the home theatre receiver set too high. I even started to adjust it (I normally put it at 3.6 metres, compared to the 2.7 metres for the front speakers). Then I realised that at a delay of just 3 milliseconds per metre, this really wasn’t going to make much difference.

But this did get me thinking along the right lines. A week or so ago I was using some video gear that seemed to insert a significant delay to the video, to the point where there were lip sync issues with some material. I’m not especially sensitive to lip sync issues, so it must have been marked for it to be disturbing to me.

The receiver I was using was one of the first generation to incorporate a group audio delay circuit. What that does is insert a user-selectable amount of delay into the signal to allow you to bring the sound back into alignment with the video. I had found an 80 millisecond delay did the trick nicely.

But, it turns out, this was operating weirdly. I have my own front speakers set to ‘large’ in the receiver’s setup, but the Krix speakers needed to be set to ‘small’. That caused the receiver to extract the bass, as it should, and send it to the subwoofer instead. But it seems that the group delay does not operate on the bass sent to the subwoofer, so it was leading the rest of the sound by 80 milliseconds, or nearly a tenth of a second. I zeroed out the group delay and everything sounded as it ought to (including eliminating the mid-bass lumpiness).

Clearly this is something I shall have to check with future receivers.

This entry was posted in Audio, CD, Testing. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *