What Is Sampling Rate?
sampling-rate
The Sampling Rate is a value you will mostly find in audio and video files. It decides how much of the original sound a recording could keep. Here is what your value means.
Sampling Rate says how many times per second the sound was measured when it was recorded or encoded. Each measurement is one sample, so a rate of 44100 means the level of the sound was captured 44,100 times every second. It is given in hertz, written Hz, which simply means times per second.
Which files carry it and where the value comes from
You will find it in every kind of audio file - WAV, MP3, AAC, FLAC, OGG - and in the audio track of video files such as MP4, MOV and MKV. In a video file it describes the sound only; the picture is measured in frames per second instead.
The value is set when the sound is first digitised, by the recorder, the microphone interface or the phone, and it is set again by any program that converts or re-encodes the file afterwards. Nobody types it in.
Typical values
A handful of rates cover almost everything you will ever see:
8000 Hz- speech and telephone audio22050 Hz- low bandwidth voice and older web audio32000 Hz- some broadcast and camcorder audio44100 Hzor 44.1 kHz - the audio CD rate, and the most common rate for music files48000 Hzor 48 kHz - the standard for video, film and broadcast96000 Hzand192000 Hz- studio and high resolution releases
Reports may write the same number in kilohertz, so 44100 Hz and 44.1 kHz are the same thing.
Why it matters
The sampling rate puts a ceiling on the pitches a file can hold: a recording can only describe frequencies up to half its sampling rate. At 44100 Hz that ceiling is 22050 Hz, comfortably above the roughly 20 kHz upper limit of human hearing, which is exactly why the CD rate was chosen. At 8000 Hz the ceiling is 4000 Hz, and that missing top end is why telephone audio sounds muffled and why an s sounds like a hiss.
It also drives file size in uncompressed formats, where doubling the rate doubles the amount of audio data for the same length of recording. And it drives compatibility: some devices and codecs accept only certain rates, and a file whose rate is misread plays back at the wrong speed and pitch, the classic chipmunk or slow motion effect.
One thing a high number cannot do is repair a poor recording. Converting a 22050 Hz file up to 96000 Hz makes the file bigger without bringing back any of the detail that was never captured. This field carries no personal information.