November 24, 2006

HARD COMPRESSION, SOFT COMPRESSION: My earlier post on hardware compressors drew a response from Ed Driscoll suggesting that software compression is just as good. Yes and no.

I use a lot of compression on podcasts — much, much more than I use on music, where my instinct is generally to fiddle with the original signal as little as possible. (In fact, getting bolder about that is one thing that improved our sound quality a lot over the first several episodes). And I do the compression on the .wav files in the computer. But I also use hardware compression on the input side, mostly so that when somebody laughs, coughs, etc., it doesn’t produce a peak signal that’s loud enough to produce distortion. I could accomplish the same thing by just recording at a lower level and then boosting levels on the .wav file in the computer later, but I find it’s always best to start with a good, loud, clean signal — you can do a lot in the digital realm, but you can do a lot more if you start out with a pretty good signal to begin with.

As with the noise reduction software — Ed likes Soundsoap, which is for the Mac, I get the same thing with the noise reduction routine in Adobe Audition — there are limits to how far you can go without introducing artifacts. When we do the podcast interviews by phone I always record a few seconds of silence up front (which is really a few seconds’ sample of the telephone line noise) and then, when processing later, I sample that, tell Audition to take out everything that sounds like that, and generally produce a pretty dramatic improvement. Nonetheless, I try to start with as little noise as possible. The noise reduction is pretty good — when we interviewed Michael Zemel in his office, there was a loud air conditioner outside, and the noise reduction removed that so efficiently that you could hear the room reverberation when we talked, something that was completely masked by the air conditioner noise on the original file. But that was taking it about as far as it would go. My own philosophy of signal processing, unless you’re deliberately trying to produce something distorted and weird, is that less is more. Not everyone agrees, of course, but the better the signal you start with, the more room you have for fiddling with it later.

UPDATE: Ed Driscoll emails that Soundsoap isn’t just for Macs, and he’s right. Sorry — I hadn’t realized there was a PC version, too.

ANOTHER UPDATE: Boy, write about music-geek stuff and the email pours in:

Tom Spaulding here, guitar tech for John Fogerty, currently with Hall and Oates on their promo tour for their excellent Christmas CD “Home For Christmas”. I’m blogging that tour at Caught Up In The Fable.

I agree with most of your take on signal processing, but you might get better results in eliminating air conditioning noise by using a high pass filter on your interview mic. I’m sure you are aware of the “bass
roll-off” switch on most microphones that typically attenuates the amount of low end (100hz or lower). There’s not much useable info down there in a voice interview and eliminating it at the source (the mic) will let the algorithm of the software noise reducer work more efficiently in removing the rest of the noise.

I tend to favor the Waves De-noiser plug-ins in Cubase and Nuendo…very useful. Another good hardware compressor that can be bought cheaply is the half-rack dbx 163X. Ebay has them for around $50-100 dollars: one slider that reads “more” is all you need!

Yes, I keep the roll-off switch on on the Edirol all the time, and will probably never remove it unless I record a concert or something. And check out Tom’s blog for lots of cool photos and guitar-geekery. I should note that Bob Britt, who’s playing as Fogerty’s second guitarist at the moment (or at least when I saw him on an MHD special recently), is really, really good.

ANOTHER UPDATE: Reader Lawrence Faria emails:

Having John Fogerty’s technician confirm your compression tactics is heavy duty confirmation that you really know what you’re doing. I’m surprised, though that in the discussion of your instinct to preserve as much as possible of the original signal didn’t include getting the best possible signal with the best possible microphone.

In an October 28th post, you mentioned your experience with your brother’s old Western Electric phone. You mentioned you wish you had one. Bill Quick noted that post, and added that they often turn up at Goodwill and the Salvation Army.

If you want one, you now have a place to look for one of the most durable products ever made. If you can arrange to have an university official see you rummaging around in those places, you might even get a pay raise out of it.

Heh. Alas, though, it’s the phone that our interviewees are talking on that raises problems. On my end, it’s a fairly decent AKG C3000 condenser microphone.

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