Can I reduce mp3 file size?

[Gideon]

I exported a podcast to mp3 and got a file that was 23 MB. My Drupal website objected and told me 5 MB was the limit. So here I am, trying to figure out how I did it before, because a few years ago I produced some podcasts and they came out the other end at about 5 MB? hmmm?

Soooo, any ideas how to compress these things? And do I pay a price with quality?

[kozikowski]

And do I pay a price with quality?

Of course. Everything MP3 does sacrifices quality. The best you can ever do is minimize it.

The worst thing you can do is make an MP3 from another MP3. The compression damages add up. You can get into trouble pretty easy. If you have a 128 quality MP3 and you cut it into a show and export it 128, the real show quality will come in something around 64.

When you make the MP3 in Audacity 2.1.2, There will be an option panel or a built-in info panel during export where you can change the compression quality. The fuzzy rules are 32 for mono, 64 for stereo are the lowest you can go before everybody notices Something Wrong. I don't know of a way to predict the filesizes. I just experiment.

If all you're going to do is cut and simple edits, you should probably use one of the pure MP3 editors rather than Audacity. They don't have the re-encoding step and their sound damage doesn't increase. If you need heavy editing and effects, you're stuck.

We warn people never do production in MP3. Record your podcast and cut it in WAV. Use WAV for the archive storage and only then make the MP3 for posting. If you have to make a correction or change, do it to the WAV, and make a whole new MP3.

Koz

[cyrano]

a few years ago I produced some podcasts and they came out the other end at about 5 MB? hmmm?

A few years ago, streaming had a lot lower bitrate. And podcasts were shorter. So I'd guess that the resulting file would be smaller.

And like Koz explained, it's all in the quality. With a lower bitrate, the file will be smaller.

[Gideon]

My podcast is 25 minutes long, mono, 22050 hz, 32 bit float.

Excuse my ignorance, but I presume bitrate refers to 32 bit float. So I plan to experiment. Should I export to wav and play around with the wav file, then re-export the wav file to mp3? Is that the procedure?

[kozikowski]

No the 32-bit float is the sample rate. How finely and accurately does the system hack up your analog sound to turn it into digital. 32-float is fantastic overkill. Audio CD quality is 16-bit. So is digital television.

Why did you decide on those sound specifications? They're really odd.

Bitrate is the number of bits required to transmit your show. As a completely stupid example, suppose you and a friend knew when you said the number "4" that really meant The Gettysburgh Address. All of it. So when you get "4" in a text, that really means whole Gettysburgh Address. That's compression (a stupid example).

In reality what happens is the MP3 system rips your sound apart and figures out the absolutely minimum amount of data you would need to put it back together at the other end. MP3 quality is not perfect. If MP3 thinks it can ignore some of the sound because you're not likely to miss it, it gets ignored. That's compression distortion. It gets worse as the MP3 quality value goes down.

That's why MP3 is dangerous to use in production. It's constantly dropping little pieces here and there, and sooner or later, you're going to notice.

Koz

[Gideon]

No the 32-bit float is the sample rate. How finely and accurately does the system hack up your analog sound to turn it into digital. 32-float is fantastic overkill. Audio CD quality is 16-bit. So is digital television.

Why did you decide on those sound specifications? They're really odd.

I just started recording and those were the specifications that came up.

So for recording a spoken address in a public hall, what specifications should I use? I see 'Project Rate' at the bottom of the screen. Should I set that at 16000 kH? As for the 32-bit float, where do I change that to 16-bit (or less)?

[kozikowski]

I just started recording and those were the specifications that came up.

Don't need the red face. That's perfectly valid.

The work window in Audacity has the shortcuts. The real settings are in Audacity > Edit > Preferences.

Attach 1
That's where you set stereo.

Attach 2
That's where you set Sample Rate and Bit Depth.

Those are my settings. Audacity will automatically convert to 44100, 16-bit on export unless you stop it.

My personal variation is 48000 instead of 44100 if I know I'm working for a video editor. Most of them don't care, but it gives me a warm, fuzzy feeling.

Can't have enough warm-fuzzy.

There is a place for super high sample rates and bit depths, but neither of us will be shooting Kanye West anytime soon, plus, that may take a more powerful computer than either of us own. Past that, those settings work really well.

Sub-sampling and lower bit depths are sometimes required for corporate telephone answering systems and other oddball, out of the ordinary applications.

Run away.

Koz

[kozikowski]

Love the bible, by the way.

Good work.

Ko

[cyrano]

There's that 32 bit confusion again...

32 bit is Audacity's internal format. It's higher than "physical" formats, to gain room for calculations. You can export in 32 bit, fi for mastering, to go to another DAW without converting. Besides that fringe case, you NEVER export 32 bit. A lot of simple players can't play 32 bit anyways. And it takes twice the disk space.

When you "physically" record, your audio interface is either 16 or 24 bit. Those are the "physical" formats. As this is partly analog, you need to watch the noise floor. 16 bit gives you a (theoretical) noise floor of -96 dB. 24 bit gives you -128 dB.

When recording a podcast, use 16 bit. There is no need to go higher, as your source is 16 bit. There is no real "recording", as the signal doesn't leave the digital realm. It's a copy from one bitstream to another. No loss and nothing to be gained by using higher bit depths.

When recording (multitrack) music to mix and manipulate, use 24 bit. That'll give you room for mixing and effects.

When exporting for playback only, ALWAYS use 16 bit, either 44.1 or 48 KHz. The 48 KHz is for anything video. There's no sense in "higher" formats.

The only reason you need to know all this, is because you need to avoid unnecessary conversions. Your computer will convert automagically between most, but not all formats. Windows Media Player, fi, has no problem with 32 bit, but has a lot of problems with 24 bit...

[Gideon]

Thank you for all the help. Im getting the hang of it now.

Just one more question. When exporting podcasts to MP3 (after recording at 44100 Hz) is there any advantage compressing the Hz rate to 22050 Hz?