Sample Rate

Sample Rate

(Sometimes called bit-rate, though that is not the same thing)
This is the number of times your audio waveform is measured (sampled) per second. So at the ‘red book’ standard for Compact Disks, the sample rate is 44.1 kHz or 44,100 slices every second.

Many of the recorders on this site can sample at 96khz. This enables 96,000 slices of audio to be sampled each second.

The new standard for studio mastering is 192kHz. Yes, that’s 192,000 samples at 24 bit resolution each second. Why would you want to sample at this rate? Well, at 48kHz due to something called the Nyquist theory (I wont mention it again), the highest frequency (pitch) that can be recorder is half the sample rate, so that would be 22kHz. This is just above the range of the human ear.

So why sample at 96kHz, or even 192kHz? Well one reason is that this allows for studio effects to work better. Another is the ‘moire’ effect, similar to the patterning that you sometimes get on tv, where a newsreader is wearing a tweed jacket that bursts into a kaleidoscope of colour, due to the jacket almost matching the definition of the dots on the tv. A similar effect can cause a ‘harsh’ sound at CD sampling rates of 44.1kHz, which only provides 2 samples per cycle of the waveform at the highest recording frequency.

Using a 192kHz sample rate allows sampling of frequencies up to 96kHz, which is about four times the range of the human ear. A good compromise, especially for portable recording, is to use 96kHz sampling. This makes less demands on your storage space, whilst still providing something close to a ‘High Definition’ recording.

Where you want to record a stereo / four track / multi track  image, 192kHz sampling has clear advantages, because the high sample rate means  reduced phase errors, with sharper leading / trailing edges on the resulting waveform which gives a more precise location for each instrument, or source of sound. The less often you sample per second, the less defined the stereo positioning. So go for the highest sample rate available if you want to hear exactly WHERE everything is. (in other words, if you want high definition).

It could be argued that bit depth increases dynamic range, improving ‘headroom’ (signal to noise ratio), whereas sample rate increases detail, improving stereo imaging and sound quality.

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Tags: bit rate, headroom, High Definition, sample rate

This entry was posted on Friday, May 29th, 2009 at 2:57 pm and is filed under Digital Audio Basics. You can follow any responses to this entry through the RSS 2.0 feed.