Compression Fun

[kozikowski]

I have two short WAV sound clips of the same show. Each one is just over 5MB download.

http://www.kozco.com/tech/audacity/CarT ... st-852.wav
http://www.kozco.com/tech/audacity/CarTalk-KPCC-852.wav

The object, using any platform and any version of volume compression, is to turn one into the other. The PodCast is lovely, the PodCast is convenient, but the PodCast has one problem. It has the dynamic range and production volume of the original studio show. This is normally very cool, but doesn't work too well in the car. The KPCC version of the same show has been through the KPCC transmitter compressors and not only it is a lot more even, it's louder and at least in my car, matches the volume of the live radio stations. Just touch buttons instead of needing to constantly adjust volume.

I included the music segment because those are particularly hard to manage without bass note pumping and other music compression distortions that don't seem to be there in the radio version in spite of the loudness differences.

Traditionally, in the olden days, we had two tracking stereo compressors. One was a fast peak limiter and the other was a sloppy, long term compressor. One would gently set overall volume and the other would tame the sharp peaks that the first would miss.

You could watch the needles move during the show and tell which announcer was good at running their sound board and who wasn't by how much work the boxes were having to do.

Koz

[steve]

Chris’s dynamic compressor does a pretty good job.
http://pdf23ds.net/software/dynamic-compressor/

Push the "Compress Ratio" up to about 0.75 and leave all the other settings at the default.

Note that there is a minor bug in it that can cause clipping on the last few milliseconds of the track. If you have this problem, just generate a couple of seconds of a tone at the end of the track, then trim it off after using the compressor.

The effect is listed in the Effects menu as "compress dynamics".

Note also, that to get it to sound the same as the KPCC version you will also need to Eq it a little to brighten it up a bit.

[steve]

I used this Eq curve:

Code: Select all

<curve name="koz">
		<point f="20.000000000000" d="-2.800000000000"/>
		<point f="95.496546225092" d="-0.100000000000"/>
		<point f="130.223507360123" d="0.157142857143"/>
		<point f="280.697924391542" d="-1.257142857143"/>
		<point f="371.133401822934" d="-1.192857142857"/>
		<point f="2369.225893131248" d="1.530991368792"/>
		<point f="5148.556262083510" d="1.957142857143"/>
		<point f="15503.859979709296" d="1.498954118219"/>
		<point f="22049.999999999978" d="1.104369440670"/>
	</curve>

followed by Chris's compressor with "Compress Ratio"set to 0.77

You can download the result here: (FLAC format 3MB)
http://easyspacepro.com/audacity/examples/CarTalk.flac

[kozikowski]

I wondered about that. The KPCC feed is basically a 15 KHz broadcast sound feed from NPR to my house. Various satellite and transmission media in the middle, but basically sound.

The Podcast feed, even though it has the pre-transmitter Mixing Desk sound, has been through KPCC's streaming audio servers. Technically, it's not the real podcast. That comes later around midnight Sunday-Pacific. The streaming feed arrives some 15 seconds after the live air show. No, I have no idea why it takes that long--and it is a guess. I didn't stop and time it accurately, but I was shocked how long it was between the music on the "live" feed and (one potato, two potato...) it arrived in the browser. I wonder if that was a result of a large number of people connecting.

I know it's not the same thing, but the difference between the analog and digital television feeds is about a second or less.

I'll need to assemble these tools some time when its not midnight.

Koz

[waxcylinder]

I know it's not the same thing, but the difference between the analog and digital television feeds is about a second or less. Koz

Same thing with Analog v. digital radio here in the UK (though slightly longer tan a second IIRC). It drives the Radio 4 listeners wild with agitation when the pips (UK time signal, synchronized from Greenwich/Rugby) arrive at different times on their different radios .....

WC

[steve]

The object, using any platform and any version of volume compression, is to turn one into the other.

Just wondering how you got on Koz. Did you find the tools, and did those settings work for you?

[kozikowski]

Not yet. I really need to deal with this.

I've actually been socially active after work and then there's that thing with Leland. We don't talk about that very much....

Koz