Chris's Compressor effect on CD burns???

Special Interest Groups Audio Processing
1

The other day I burned 5 CDs. Each CD contained the same 27 songs and each was burned with the same program–ImgBurn with the same batch of CD-Rs (Taiyo Yuden) at the same speed (16x). The burns were just intended to be tests of Chris’s Compressor and WaveGain.

Two of the 5 CDs contained the 27 songs as compressed by Chris’ Compressor (one at .5, the other at 1.0 compression levels).

I just got around to playing them in the last hour.

The 2 CDs burned with Chris Compressor material are defective.

All songs on those 2 CDs play at maybe 10 times normal speed, going through a 2.5 minute song in less than 15 seconds. Too fast to be intelligible at all.

This happens when played back with Windows Media Player and with Media Player Classic.

If it matters, this was with the standalone version of Chris’s Compressor, not the Audacity plug in.

I have never encountered this “fast playback” issue under any circumstances and have never even heard of such a thing. If you asked me to repeat it deliberately, all I could do is try another attempt with Chris’s Compressor and see what happens.

The files appear normal in Windows Explorer–track 1.cda, track 2.cda, etc.

What gives??

I have difficulty believing it is a coincidence, but I guess anything is possible.

2

More info:

Playing the individual compressed tracks directly from my HD rather than from a burn gives a slightly different result. The songs still play through in about 14 seconds, but the elapsed time indicator in Media Player Classic progresses quickly from zero to the full 3 minutes length, rather than from zero to 14 seconds when playing from the burn. But they are still totally unintelligible.

So–the compression process is doing something bad to the songs, completely aside from burning. The compressor throws no error messages during the compression process and apparently completes successfully.

I just did another burn of the compressed files with the same bad result.

I also noticed the following:

When loading the songs into ImgBurn, I noticed that the expected “analysis” progress bar for each song only spun up to maybe 10%, rather than the expected 100%. The entire burn and verify process took only maybe 2 minutes when it normally takes 7 or 8 minutes. I get no errors at all and the verification completes normally.

I cannot tell if what I hear is the entire 3 minute song played back in 14 seconds, although that is what it sounds like–like a very high speed audible scan.

If it is the whole song, I cannot explain why the burn took so little time. I can’t understand why it would not be the whole song.

This is on Windows 7 using the latest available standalone version of the compressor (version 1.2.1, apparently from October 2008).

I don’t know at this moment if the Audacity plug-in version behaves differently.

3

I only use the Chris that installs as a plug-in to Audacity. I don’t know of anyone that’s had problems when they did that.

Somehow, Chris produced damaged files. Either the burner doesn’t understand them, or the INFO inside the file and the actual music are different. Either way, they’re toast.

Koz

4

I’ve also only used the Audacity plug-in version.
It could perhaps be a file format issue. Are you using 16 bit stereo 44.1kHz WAV files throughout the process?
If it’s not to do with that, then I’d suggest that you either try the plug-in version (which we may be able to help with), or ask Chris about it through his web site.

5

Steve:

Yes, I am using the standard 16 bit, 44100 setting throughout.

Since my post, I did more testing with these results. This is just an FYI and may be no surprise to any of you.

The Audacity plug in version works without incident on Windows 7. However, I am discarding it for the following reason.

I made a CD of 27 random tracks using the Audacity version and the maximum 1.25 compression setting, just to see the effect. On about half of the tracks, I noticed volume swells–sometimes in the middle of a song, but most often in the final couple of seconds, as the last struck note or vocal decays. In a couple of cases, I noted a similar effect on an intro.

Not good. It’s as if you suddenly turned the volume control up in the last few seconds–quite obvious and on about half of all songs.

There may be something about the half with the issue that differs from the half without the issue. I don’t know what that would be. These were mostly vocals, a few instrumentals, and none had “odd” tails or fades when listening to the uncompressed versions.

It may be that a lower compression setting would avoid this volume swell issue–I don’t know. But I am interested in lowering the number of steps needed to burn a CD with equal volume across songs, rather than increasing the steps. I don’t want to have to fiddle with compression settings song to song in hopes I might have some success at that, even if it did eliminate volume swells.

I’m not interested in compression because I like compression–I don’t like it. But I thought it might be tolerable as a way to get approximately equal loudness from a series of uncorrelated songs on a burned CD. I saw nothing in my test that inspired any confidence.

I also tried WaveGain on a burn of the uncompressed versions of the same songs. I could not detect any improvement–the songs still had the same volume differences as I had noted on a CD containing unaltered versions.

So, it would appear that the only solution is manual adjustment of a few tracks after a test burn. Not particularly surprising.

6

That is supposed to happen.
As it says in the text at the top of the plug-in:

…‘Compress ratio’ is how much compression to apply. Raise when soft parts are too soft, and lower to keep some dynamic range. You can soften the soft parts instead of increasing them with values < 0, > and invert loudness with values > 1

So with values greater than 1, if there is a long slow decay then the volume should swell.

7

Steve:

Thanks for the comment. I may or may not try again.

I had not seen the note you posted.

I did find it curious that the standalone version has a max setting of 1.0, while the Audacity version extends to 1.25.

I assumed going from 1.0 to 1.25 would just be more of the same. Inferring from your post, maybe not.

8

It is.

As you increase the compression level, the quiet bits get louder until at a setting of 1.0 the loud parts and the quiet parts (as long as they are above the “noise threshold”) should be at about the same volume. As you go beyond a setting of 1.0, the quiet parts overtake the loud parts so that the previously quiet parts will be louder than the original loud parts.

An old saying: “If at first you don’t succeed, read the instructions.” :wink:

9

I agree about reading instructions–I had not done it.

But I have now, and am not entirely clear on them–or at least I don’t understand all the options such as floor, hardness, etc.

But I am trying a new burn with default setting (.5 compression) and we’ll see how it goes.

I have never attempted batch processing aka chains. A quick look at it shows a bunch of effects that can be added. I do not see “compress dynamics” listed—can I infer you can’t batch Chris’s compressor?


On an unrelated note:

I had previously mentioned oddities when renaming, such as being told in an error message to the effect that the chosen name lacked an extension.

Well it turns out that occurs on file names such as:

T. Boone Pickens - I’m An Oil Drillin’ Daddy

or

Boone Pickens - St. James Infirmary

Both would get the error. The oddity in both names is the abbreviated T. and the abbreviated St.

I guess any dot in the name is verboten. But easily worked around by manually adding an extension.

10

Believe it or not you’re using the simplified interface :open_mouth:
Previous versions of Chris’s Compressor had much more cryptic controls - the old interface can still be enabled in the current version by a couple of minor edits to the code, and offers greater control over the effect.

The default settings generally work pretty well.
If you want a “stronger” effect, the first slider (Compress Ratio) can be increased a bit. Settings between 0.5 and 0.7 usually work pretty well, though if you want to really “flatten” the dynamics you could push it up as high as 0.8.
Compress Ratio = 0.5 gives quite a subtle effect, evening out the dynamics without it being noticeable that there is an effect being used.
Compress Ratio = 0.7 is very close to the compression that is commonly used by radio stations. It’s will even out the dynamics quite a lot while still not being too noticeable.

The “Hardness” setting replaces a whole bunch of sliders in the old interface (with wonderful names like “Release exponent”).
Basically what this control does is to adjust the “speed” of the effect.
At lower (soft) settings the compression will adjust the output level very gradually - like manually adjusting the volume knob on the amplifier slowly.
As higher (hard) settings, the compression will react more quickly - like manually turning the volume knob more quickly.

Correct. Audacity can currently only batch with built in effects and not with plug-ins. For the “Chains” command to know about the existence of an effect, support for the effect must be hard coded into the batch processor. There has been a feature request for batch processing to be extended to other effects, but there has been no movement on that yet.

Correct. When Audacity sees the dot it assumes that characters after it are going to be the file extension.
Many other (non alpha-numeric) characters will also cause problems so it is always safest to stick with letters, numbers, hyphen and underscore. These characters should work on any computer.

11

Steve:

Thanks for the continued help.

I just burned a bunch of songs with Chris at default setting except I chose .98 amplitude on the output rather than .99.

I am generally happy with the results except for one song. It still plays noticeably louder than the other 32. The other 32 do not differ noticeably in volume. Before this default compression test, there were 4 or 5 that had slight noticeable differences–so the compressor is having some desirable effects.

After compression and before compression waves for that still problematic song are shown here.

Do you see anything in the before waveform that would lead you to believe it might still be louder than the others after compression—i.e., not react as the other songs did to compression and amplitude choices in Chris? The song is question is a circa 1960 country recording.

Entirely possible my technique is bad—given that my goal is equal volume across 33 tracks, should I be running all 33 through a compressor—or only certain songs (the quiet ones, the loud ones, whatever)???

If that is true, it may be less labor-intensive to not use a compressor at all and go back to the old manual “test burn and then adjust a few songs for a reburn”.

The remedy for that one song might be to compress it more or less than the others, but then I am back to trial and error and fiddling–which I had hoped to avoid.

Any comments appreciated.
roy counts wave compressed at default.JPG
roy counts wave uncompressed.JPG

12

The levels in that song are fairly constant throughout (very little dynamic range), so all that has happened by running it through the compressor is that the volume level of the entire song has been raised a bit.
The waveform also looks quite “dense”, so it is likely to sound louder than songs that have an equal peak amplitude but more variation (more of the audio at a quieter level and less peaking up to the average level of this track.

What I do is that I’ve got a Behringer UCA-202 USB sound card (about $25) that I can plug into my computer, then connect to my music system. This means that I can listen to the tracks through my music system before I burn them to CD. I would normally listen to the tracks while they are on the computer (through my music system) and adjust the levels using the volume slider in Audacity so that it roughly matched my “reference” level.

I would only tend to use compression on tracks that were generally low volume but could not be amplified up to the same “loudness” as the other tracks due to having a few exceptionally high peaks (which would distorted if I tried to increase the level further). What the compression effect does with that type of track is to raise up the level of the quieter parts without increasing or distorting the loud peaks. Thus the track overall sounds louder and matches the other tracks better.

13

Gotcha.

I’ve got a Behringer myself–the variant with the turntable input.

I think pre-listening through a sound system is probably the better alternative, considering virtually every CD I burn has a song or two that needs adjustment. Better to fully evaluate before the burn rather than after.

I just don’t tend to notice minor volume variations in shuffle play among thousands of songs on a hard drive like I do on playback of a 25 or 30 songs from a CD. That might be because I often use HD play as background noise, but listen more attentively when I choose a CD.

Nor do I recall going through this unequal volume business 20 or 30 years ago when I was constantly making cassette anthologies from vinyl and a turntable. But of course in that case, I was feverishly attentive to VU meters and today I am largely taking mp3s as I find them.

Thanks again–I do appreciate the insights.