
Apple Lossless
Apple Lossless (also known as ALAC (Apple Lossless Audio Codec), or ALE (Apple Lossless Encoder)) is an audio codec developed by Apple Inc. for lossless data compression of digital music. Apple Lossless data is stored within an MP4 container with the filename extension .m4a – this extension is also used by Apple for AAC audio data in an MP4 container. However, Apple Lossless is not a variant of AAC (which is a lossy format), but rather a distinct lossless format that uses linear prediction similar to other lossless codecs such as FLAC. All current iPods, iPhones, and iPads can play Apple Lossless–encoded files.
Sample Rate
Sample rate is the number of samples of audio carried per second, measured in Hz or kHz (1000 Hz). 44.1 kHz is the sampling rate of audio CDs and 48.0 kHz is commonly used for professional video. Higher sample rates result in higher quality audio with larger file sizes. Setting this to Auto will create an output file with the same sample rate as the input file. If the output file does not support the sample rate of the input file, Pro Audio Converter will use the greatest sample rate that is supported.
Bit Depth
Bit Depth defines the numer of bits (1's and 0's) used to represent each sample.
By increasing the bit depth, quantization noise is reduced improving the signal to noise ratio. For each 1-bit increment in bit depth, the S/N will increase by 6dB. 24-bit digital audio has a theoretical maximum S/N of 144 dB, compared to 96 dB for 16-bit. Audio CDs use a bit depth of 16 bits. 24-bit is common in professional audio and video environments.
Channels
This defines the number of audio channels contained in the output file. Setting this to Auto will attempt to create an output file with the same number of channels as the input file, if it is possible. You can also manually set it to output Stereo (2 channels) or Mono (1 channel).
Quality
Since Apple Lossless is a lossless format, the quality setting only has an effect on the file size, not the audio quality. Higher quality settings will take longer to encode but result in smaller files.