Recording Options

   With Audio Hijack Pro, you can record audio to four different formats - AIFF, ALAC (Apple Lossless), MP3 and AAC. Each of these four formats also has many sub-options, and we've detailed many of the various recording options below. First, let's examine what format is right for you.

Which Format Is Right For Me?
   There are a lot of audio formats and options in AH Pro. If you don't know what you're looking for, a safe bet is to record to MP3 or AAC. Both of these compressed audio formats result in medium to high quality files and use low amounts of disk space. So, what bitrate do you need? If you're recording spoken word, a very low bitrate will still sound great. If you're recording music, 128 or 192 kbps is a good place to start. Just remember, as you lower the bitrate, you lower both the quality and the amount of disk space being used up by the file. Experiment and find what the best tradeoff is for you.

If you're burning to a CD or planning to edit the file before you use it, save to AIFF. If you want a perfect quality copy but don't want to use all the disk space of AIFF, use Apple Lossless - it's compressed, but it's an exact copy of the audio as it was received.

Bookmarkable AAC, ALAC and MP3
   AAC, ALAC and MP3 files can all be recorded in a so-called "Bookmarkable" format. This means that when you play them in iTunes or on an iPod, they will resume from where they were last stopped. If you record an hour long radio program, this can be very useful. When you're listening, you can stop the program halfway through, come back the next day and hit play, and it will automatically start right where you left off. To make a Bookmarkable recording, use the AAC or MP3 bookmarkable presets or a Custom AAC, ALAC or MP3 format.

Bulletproof MP3 And AIFF Recording
   On OS X, applications crash a lot less often than they used to. But bugs and kernel panics still happen, and if you're in the middle of a recording, this can be a huge setback. With Bulletproof MP3 and AIFF recording, Audio Hijack Pro constantly updates the saved recording, so if you have a crash, you won't lose any of the previously recorded audio. All MP3 and AIFF recordings are bulletproof, so just choose an MP3 or AIFF format to use this feature.

CBR vs. VBR vs. ABR
   MP3 recording has 3 different sub-formats. CBR will work in any MP3 player but is a bit inefficient, while VBR and ABR offer a bit more in the way of overall performance, but may have problems in some older mp3 players. In short:

   CBR (Constant Bit Rate): The amount of disk space per second of audio is set prior to recording and used for the entire file, regardless of how complicated parts of the audio are. Thus, some portions get less space than they need, and others get more than they need. Compared to the other formats, it's less efficient, but it uses the least CPU and is universally recognized.

   VBR (Variable Bit Rate): Each portion of audio is given the amount of disk space it needs, within a set boundary. This will give the best sound quality of the three, but some software won't recognize it or play it properly.

   ABR (Average Bit Rate): The disk space used is an average of what's needed for the entire file, so the portions which need a lot of space will get more and those that don't will get less. This is the least universal format, but it's a good technical compromise between CBR and VBR.

For more info, see http://lame.sourceforge.net/doc/html/modes.html

MP3 Quality Sliders
   Custom MP3 Formats use one or both of the Quality sliders seen in the Custom sheet. The higher the quality, the better the audio file will sound, all without using more disk space. The tradeoff here is that it will use more CPU power in encoding. VBR will also use the VBR Quality slider. The higher this is set, the more the file will fluctuate from the chosen bitrate. This means that portions of audio that need more disk space are more likely to get it. Again, this requires more CPU.

Lossy vs. Lossless
   When doing audio encoding, the goal is to save space over the raw audio. MP3 and AAC are very good at this, reducing file size down to about 10% of the original audio. However, these are "lossy" formats - when you record to them, some of the original audio data is lost. Often, this goes unnoticed, but if you hear artifacts in the audio or if you need perfect quality recordings, consider AIFF or ALAC - these formats are both "lossless", meaning all the original audio data is there. In the case of AIFF, the file size is not compressed at all. ALAC uses about half as much disk space as an equivalent AIFF, which is a large savings but still results in very large files compared to MP3 and AAC. Further, ALAC is not nearly as universally accepted as AIFF.

AIFF 16-bit and AIFF 24-bit
   AIFF 16-bit is the universal audio format on the Mac - almost every single application that deals with audio can read AIFF files. AIFF 24-bit is a pro-audio format which is an improvement over AIFF 16-bit in terms of quality, but takes up more hard drive space, and is much less compatible. Unless you know that you need AIFF 24-bit, AIFF 16-bit is the recommended AIFF format.