Audio File Quality Definitions
COMPRESSION QUALITY DEFINITIONS
It's important to understand these following terms. Choosing the appropriate path has a significant effect on your options and outcomes.Uncompressed
A file's data is stored as-is in full original format, and it doesn’t require decoding. This provides the widest range of use and quality, allowing for excellent editing and manipulation through effects. It results in much larger file sizes.
Compressed
A file is processed to carry less data for the purpose of making the file size smaller. Compression reduces the file's range of soundwave frequency. To achieve more compression, the process deletes information. The Mp3 and Mp4/AAC compression process creates "empty" frames without audio data, which make them unusable for editing purposes.
Compression requires decoding in order to read it correctly. This is usually invisible to the user, because compression-reading codecs are now part of every audio-friendly device. You can play Mp3s on pretty much every device because that codec reading ability is now built in.
Lossless
This is an UNCOMPRESSED FILE FORMAT. This file format has no data loss whatsoever, is the uncompressed type of file, and therefore creates larger file sizes.
Lossy
This is an COMPRESSED FILE FORMAT. It's a lower quality file that lacks the original amount of data due to compression treatment. A lossy type file does not mean that it is unusable for general listening, but it is limited in its range of sound quality, and is not meant to be used in an editing environment.
Comparing terms: Compression is about an action taken on a file, while lossy is about the quality of the resulting file.
---------------Kilohertz: A kilohertz (kHz) is a unit of frequency equal to one thousand cycles per second. Hertz measure cycles per second, and kilo means one thousand.
- CD quality audio is set to 44.1kHz
- Standard aniamtion film sound is set to 48 kHz
- Professional musicians will record sound from 96 kHz and higher.
Sample Rate: This is the number of digital samples taken from an analogue file within in one second. The more samples there are, the finer the quality of the digital sound result. The higher the sample rate, the larger the file size.
When recording, mixing, and mastering, it's always to your advantage to work at the highest sample rates and bit-depths possible: 48 kHz, 96, kHz, or even 192 kHz. This provides greater resolution for audio mixing and effects, and gives the flexibility of bouncing down to a sample rate that works the best with your medium of distribution (mobile devices or professional theatre).
Bits: Computers store digital information in 1 and 0s. Those binary values are called bits. The higher the number of bits indicates more space for information storage.
Bit depth: Bit depth for audio refers to the amount, or depth, of data that was captured every time the file was sampled. Bit rate and sample rate work together to define the sound file's resoution quality.
- 16-bit: We are able to store up to 65,536 levels of information
- 24-bit: We are able to store up to 16,777,216 levels of information
Increasing sample rate and bit depth allows you to improve the quality of the sound, but you also increase file size. Can you tell which one has more sound information as a result?
Figure A has fewer samples and a lower bit depth than Figure B.
Bitrate: This refers to how many bits are processed per second (or minute, or other measure of time)
The size of a file is determined by how many "bits" of data flow per unit of time (rate). This is measured in kilobits per second (kbps). Many people think bitrate (sample rate) is just an indicator of quality, but it's not as simple as that. An uncompressed WAV file format will have a much higher bit rate demand than an MP3, but this quality and size also depends on whether the file is a 16, 24 or 32 bit file.
- An MP3 file at 128 kbps will take up approximately 1mb of space per minute of audio.
- An MP3 file at 320 kbps will take up about 2.4mb of space per minute.
- An (uncompressed) WAV file will take about 10.6mb per minute.