Export Bitrate

[marccyfre]

I'm sure this is a fairly basic question, but I couldn't find any clear explanation in the manual or by Googling, so: I have someone who wants the file which I created in Audacity, provided to them in either WAV or AIF at 192 bitrate. First question: AIF and AIFF are essentially the same, right? Or am I wrong? Second question: I'm confused as to the definition of bitrate. This is a mono track, voice, recorded in Audacity at the default rate, Mono 44100 Hz, 32-bit float. The option to export the file from Audacity says I can export as WAV or AIFF at 'signed 16 bit PCM'. How does this translate to the '192 bitrate' desired? Thanks in advance.

[billw58]

The person to whom you are providing the file seems to have left something out. Either they want an MP3 at 192 kbps, or that want a WAV or AIF at 192000 Hz sample rate. The latter seems unlikely. And, yes, AIF and AIFF are the same thing.

So you need to ask again, do they want 192 kbps or 192000 Hz sample rate. If the former then they want an MP3. If the latter then they will receive a huge file.

The rule of thumb for a 16-bit stereo file at 44100 Hz sample rate is 10 megabytes per minute. At 192000 Hz sample rate that would be about 43 megabytes per minute. You can cut that in half for a mono (single channel) file.

To export an MP3 from Audacity you need to install the optional LAME MP3 encoding library.

Instructions are here: http://audacityteam.org/help/faq?s=install&i=lame-mp3

When you get to the download page make sure you get the correct version of LAME for your version of Audacity. I note that you have posted in the 1.2.x section of the forum. I'd recommend downloading the latest 1.3.12 version http://audacityteam.org/download/beta_mac as it has a lot more features, and works better with OS X 10.6. You can have 1.2.x and 1.3.12 installed at the same time, but you can only run one at a time. Version 1.2.x will not open projects saved in 1.3.12.

-- Bill

[marccyfre]

Many thanks, Bill. I thought that what they were asking for didn't quite make sense, but I don't know enough (yet) to be certain.

I accidentally posted in the Audacity 1.2.x section, sorry. I do have (as of last week) Audacity 1.3.12 (beta) and had downloaded the Lame library, which has worked fine when I've exported files as MP3's.

Thanks again for your explanation.

[kozikowski]

The two specifications talk about things important to the people using them. The sample rate and the bit depth reflect directly on the quality of the work. 44100, 16-bit, Stereo is the specification for Music CDs. The slightly higher 48000, 16-bit Stereo is the specification for television sound. Studio recordings go up from there for even higher quality.

You can figure out the bitrate for these files, but that's largely irrelevant to the people using them.

MP3 and other compressed files tend to feature the transmission bitrate because file size and speed tends to be important over quality. Email systems will only let you send a certain amount of data.

Sometimes the fact that these formats get the high speed and small files at the expense of quality is a nasty surprise. Some of the more serious, modern compression systems change specifications during the performance, so the bitrate might the only useful number to describe the work.

Koz

[marccyfre]

Thanks, Koz – I'm interested in learning.