Absolute db levels in Garageband mp3 files

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Absolute db levels in Garageband mp3 files

I just started using Garageband as the basis for a radio show. I realize it is not necessarily meant for that purpose, but it certainly does the trick for simple editing of interviews (from iChat, phone, or H2 Zoom), adding jingles, moderating with a good studio mic (no troubles with interfaces, stange noises or cheap mics), and importing MP3 songs from my private collection in iTunes. The file goes into a professional system and is broadcast on the Internet so they don't need a lot of effects from Garageband. I realize that everything is relative in Garageband as all of the tutorials just mention doing stuff "until it sounds good". Obviously, this works fine for little podcasts and sending stuff to friends, but I was wondering if there are semi-professional ways to get the decible levels within the standards asked for by the radio station -3db for music, -1-0db for voice. The idea is to have an even broadcast with as little editing on the sound waves as possible since radio is ongoing communication and not usually a work of art like a song. There seem to be a few factors that must work together. I end up with 2 to 4 tracks that are exported to the harddisk and sent off to the server. Here are my comments and questions:

1. Recording input level: There seems to just be a slider in Garageband '09 with no calibrations so I just keep it on full gain and use the mic gain to get a good voice recording without clipping. Is this smart? Trying to change the recording level for different things without having a reference doesn't seem like a good idea.

2. Imported MP3s (not recorded live through the system) work very well although their music wave curves vary according to the loudness of the original recording. Changing db levels of songs is possible, but not fun if you have a lot of songs from different CDs.

3. Track output: I realize this is also an indicator for the input (clipping, etc.) which immediately becomes output in the track. How do the individual track levels work with the master level? They can both be set to exact dp levels, but certainly the result is some sort of relative level. What is the result of having a track ouput slider set at -1db and the master slider set at 5db when you export your project to MP3?

4. What does the "normalization" option upon export override? Does this change the loudness within the individual tracks (hopefully raising the weak sections like the different CD qualities) first and then within the whole project, or neither of the above?

5. Should I be doing a kind of mastering process instead of just exporting to disc, or is that basically the same thing.

If the answer to all of this is to do a lot of trial and error stuff and then try to do everything the same, I will accept that. At this point, that is a better option than spending money on a professional program or spending time correcting loudness in other programs. I need to spend my time on editing the contents and making things interesting. Having said that, I would be willing to do some tweaking of whole sections if anyone can recommend a program that will allow me to see (Garageband only has +0- in its editor, right?) and edit db levels.

I hope this is not too basic and that some of the rest of you might be wondering how Garageband functions when its files venture beyond the iTunes/Podcast world. Also, it seems like a lot of questions on the forum basically have to do with the relationship between input quality and output options, which is what all this is about.

Thanks, Kent

iMac 24 ", Mac OS X (10.5.6)

Posted on Apr 21, 2009 6:54 AM

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Answer 1

Apr 21, 2009 7:17 AM in response to KJ Miller

1. Recording input level: There seems to just be a slider in Garageband '09 with no calibrations so I just keep it on full gain and use the mic gain to get a good voice recording without clipping. Is this smart?

Yes, you should max your input levels to take full advantage of the dynamic range.

2. Imported MP3s (not recorded live through the system) work very well although their music wave curves vary according to the loudness of the original recording. Changing db levels of songs is possible, but not fun if you have a lot of songs from different CDs.

If you import a sound file, it is imported "as is". So if the files come with different levels, they keep them. You wouldn't want something different without being asked, would you?

3. Track output: I realize this is also an indicator for the input (clipping, etc.) which immediately becomes output in the track. How do the individual track levels work with the master level?

The dB indicators of the volume sliders have nothing to do with the absolute value of the output - they take whatver is there and raise it by the number specified. And yes, the sliders are probably additive in the way that +1 dB in the track and +1 dB in the mix raise the signal by 2 dB, although I'm not sure.

4. What does the "normalization" option upon export override? Does this change the loudness within the individual tracks (hopefully raising the weak sections like the different CD qualities) first and then within the whole project, or neither of the above?

Normalization is only applied to the mix, and it has nothing to do with loudness. It just raises or lowers the overall level of the mix so that the peak amplitude hits a certain predefined value. Most people find GB's normalization rather useless and max out their overall levels by hand (as hot as possible without clipping).

5. Should I be doing a kind of mastering process instead of just exporting to disc, or is that basically the same thing.

That's a matter of taste. If you import professional songs from iTunes, they are mastered already, so I wouldn't mess with them too much. And spoken voice in my experience doesn't need a lot of filtering and compression, you want it as faithful as possible.

What you might do is do your production in GB, play it completely by ear until you like it, export the mix and then run it through an audio editor where you can normalize it to very precise dB levels.

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Answer 2

KJ Miller Author

Level 1

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Apr 24, 2009 7:29 AM in response to KJ Miller

Thanks Christoph

I appreciate your great answers. It helps a lot to get an idea of what is possible and what is not. One last thing for now. Does make any sense to play with the compressor levels? I assume they apply only to complete tracks and not individual sections.
Thanks again,
Kent

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Answer 3

Apr 24, 2009 7:37 AM in response to KJ Miller

Sure, play around with it! The worst thing that can happen is that you apply too much compression (like people tend too use too much reverb when they start experimenting) which might squeeze the feeling out of a track.

And no, you can't have a compression curve on a track, so it's the same setting throughout the track.

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Answer 4

Apr 24, 2009 9:31 PM in response to KJ Miller

KJ Miller wrote:
but I was wondering if there are semi-professional ways to get the decible levels within the standards asked for by the radio station -3db for music, -1-0db for voice. The idea is to have an even broadcast with as little editing on the sound waves as possible since radio is ongoing communication and not usually a work of art like a song.

The usual way people do this for broadcast is with compression or limiting. You could experiment with the compressor / limiter on individual tracks or on the master track (which effects the stereo mix of all tracks). You don't want the effect to degrade your audio, but limiting dynamic range through compression is standard for broadcast.

1. Recording input level: There seems to just be a slider in Garageband '09 with no calibrations so I just keep it on full gain and use the mic gain to get a good voice recording without clipping. Is this smart? Trying to change the recording level for different things without having a reference doesn't seem like a good idea.

Recording levels are set outside of GB, with whatever hardware you're using. So the slider in GB shouldn't effect the input level. It is a good idea to record a hot signal that stops short of distortion. I'm not sure exactly what slider you're talking about in GB, but as a starting point, I think it's usually a good idea to put it on 0 (rather than all the way up). The 0 position is considered "unity gain." Then adjust from there.

3. Track output: I realize this is also an indicator for the input (clipping, etc.) which immediately becomes output in the track. How do the individual track levels work with the master level? They can both be set to exact dp levels, but certainly the result is some sort of relative level. What is the result of having a track ouput slider set at -1db and the master slider set at 5db when you export your project to MP3?

You're right. It's relative. Also, the combined result depends on the source material.

4. What does the "normalization" option upon export override? Does this change the loudness within the individual tracks (hopefully raising the weak sections like the different CD qualities) first and then within the whole project, or neither of the above?

Christoph summed it up pretty well. To respond further, normalization doesn't effect individual tracks, only the combined master track. Theoretically it raises the loudness of the overall mix by bringing the highest point up to the highest level (0dBFS) with everything else below that. In practice, with a wide dynamic range between a loud transient and average levels well below that, it can act like a nanny switch, keeping average levels (the ones that count) low. By turning off normalization and raising the overall volume manually, you are forcing GB to distort for that transient, but it could be so brief and inconsequential, that the overall increase in volume is well worth the tradeoff. A more "pro" approach would be to insert a limiter that would make sure no transient bursts into distortion, and also reduces the overall dynamic range (so that more of it is closer to the top of the volume scale) and raises the average levels.

5. Should I be doing a kind of mastering process instead of just exporting to disc, or is that basically the same thing.

The preset and controls on the "Master Track" are GB's mastering controls. If you select appropriate presets on the Master Track, and edit their parameters to your liking, that would invoke mastering prior to exporting. That's where you could play around with compression, limiting, etc. to even out and control levels for the whole track.

If the answer to all of this is to do a lot of trial and error stuff and then try to do everything the same, I will accept that. At this point, that is a better option than spending money on a professional program or spending time correcting loudness in other programs. I need to spend my time on editing the contents and making things interesting. Having said that, I would be willing to do some tweaking of whole sections if anyone can recommend a program that will allow me to see (Garageband only has +0- in its editor, right?) and edit db levels.

Probably a lot more than you want to spend, but you might want to check out Ozone:

http://www.izotope.com/products/audio/ozone/

Izotope makes the following mastering guide (PDF) that goes along with Ozone, but it also offers good explanations you might find helpful:

http://www.izotope.com/products/audio/ozone/OzoneMasteringGuide.PDF

Good luck!

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