Audio Conversion specific for iPhone SDK Development

April 18, 2009 § Leave a comment

I slowly discovered there is very little information on Audio related to iPhone SDK development. GarageBand software is only helpful if you are recording and editing performing audio directly into your Mac. Seriously how many of you can hire a live musician or a sound technician and rent a studio for hours and days just to record a few or tens of audio or sound effects.

I am sharing experience in doing things affordable and fast on audio preparation specific to iPhone SDK developmenet. These kind of information are just not there available. At least it is not shared or published by game companies. Perhaps those high quality application companies can hire professional paying premium price for such work.

Switch offers a free version Audio File Converter for Mac OS X here. Free is good. Even if you have to pay for the software, it is worth to buy it for the time it save you from doing extra work. Typically any professional studio or audio editing software costs from couple of hundred dollars to thousands of dollars. We are going to explore the startup bootstrap way.

Switch offers a simple way to convert multiple audio files by selecting or drag and drop. The advantages are you can take actions with several clicks on multiple audio files very quickly and able to play the audio files before or after conversion.

  • MP3 encoder supports constant or variable bit rates from 8 to 320kbps with optional error correction and stereo modes.
  • WAV encoder supports sample rates between 6000 and 196000Hz in PCM as well as a number of other audio codecs.
  • Allows up to 32000 files to be converted in one batch.
  • Can be run from the command line for automation with other applications.
  • Optimized CPU usage and efficient code allows for fastest conversion times.
  • Convert mp3 to amr to load your own ringtones on your cell phone.
  • Extract audio from video files for your phone or other audio player.

These are the audio formats Switch support on Mac

  • .wav
  • .mp3
  • .au
  • .aif/aiff
  • .gsm
  • .vox
  • .raw
  • .ogg
  • .flac
  • .rss
  • .m3u
  • .pls
  • .wpl
  • .mov

The way the audio is compressed and stored is call the codec. Some file types always use a particular codec. .mp3 always use the “MPEG Layer-3” codec. “.wav” file can be encoded with the “PCM”, “GSM6.10”, “MPEG3” and other codecs.

wav – standard audio file format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files, which means that they can be large in size – around 10MB per minute of music. It is less well known that wave files can also be encoded with a variety of codecs to reduce the file size (for example the GSM or mp3 codecs).

mp3 – the MPEG Layer-3 format is the most popular format for downloading and storing music. By eliminating portions of the audio file that are essentially inaudible, mp3 files are compressed to roughly one-tenth the size of an equivalent PCM file while maintaining good audio quality. mp3 format is ideal for music storage but it is not good for voice storage.

aiff – the standard audio file format used by Apple. It is like a wav file for the Mac.

raw – a raw file can contain audio in any codec but is usually used with PCM audio data. It is rarely used except for technical tests.

aac – the Advanced Audio Coding format is based on the MPEG4 audio standard owned by Dolby. A copy-protected version of this format has been developed by Apple for use in music downloaded from their iTunes Music Store.


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