Loseless versus Lossy
In order to make a music file smaller, it must go through either lossless or lossy compression. With lossless compression, all original data from the music file can be restored after it’s uncompressed, where as lossy compression
permanently reduces the music file by cutting out some data during the encoding process. Whenever any data is lost or removed from a music file during compression, the resolution is negatively impacted.
Rates of compression
When music is digitised for downloading and streaming purposes, it is basically broken down into a series of audio snapshots (sort of like how several still frames make up a film), and our brains interpret all these snapshots together as continuous sound. The more snapshots taken, the more detail a digital music file will have.
The sampling rate is the number of snapshots taken per second when analogue sound waves are converted into digital. The bit depth is the amplitude of the waveform at each sample point (8-bit has 256 levels for each sample; 16-bit has up to 65,536 levels).
High-res audio refers to audio files that have a higher sampling rate and more bit depth than a CD. CD has a sampling rate of 44.1kHz and a bit depth of 16-bit, while high-res files have a sampling rate typically ranging between 96kHz and 192kHz at 16- or 24-bit.
Also note the term ‘bit rate’. This refers to the amount of data that is processed over a certain amount of time. So, in audio, it means kilobits per second. An iTunes song has 256 kilobits of data stored in every second of a tune. Like sampling rates and bit depths, it’s better to have a higher bitrate.
Logically if you have a higher bitrate you’re going to have more data and thus have larger files that takes up more space on your hard drive or takes longer to download.
Type of Hi-Res Files
There are several high-resolution audio file formats available with incredible sampling rates and bit-depths. Two of the most popular types are FLAC (Free Lossless Audio Codec) and ALAC (Apple Lossless Audio Codec), both of which are compressed but claim to hold onto and recover every single bit of data from a file.
FLAC files on average have a sampling rate of 44.1 KHz, a bit depth of 16-bit, and a bitrate of 1411Kbps. CDs also have a bitrate of 1411kbps, while “lesser-quality” MP3s have a bitrate of 320kbps and ITunes AAC files 256kbps.
Other formats include WAV, AIFF and DSD, the format used for Super Audio CDs