Bit depth

[Anonymous Student]

What is the effect of using fewer bits per sample to store a speech waveform?

[Simon King]

The effect is best described as a type of distortion. Using fewer bits means that the digital waveform is a worse approximation to the original analogue one. The attached samples demonstrate this (use headphones).

Tips:

• use headphones to listen
• you might need to download the files and play them outside your browser (which might not handle the 4 bit version)

• This reply was modified 10 years, 5 months ago by Simon King.

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[Anonymous Student]

I was wondering why 8bits and 16bits are used normally. I mean, will something go wrong if we choose 9-15bits?

[Simon King]

Nothing will go wrong when using any number of bits.

However, the choices of 8 and 16 are the most convenient because of the way computers store numbers. 8 bits is one byte and corresponds to a char in software (in C family languages). 16 bits corresponds to either an int or short in software.

Using 9 bits, for example, would be very inconvenient when writing software, since there is no built-in type that is of exactly that size.

Deep down in the operating system (in fact, in the hardware), everything is stored with a fixed number of bits. In modern operating systems, this is now usually 64 bits (older computers used 32 bits). The operating system can very neatly pack 8 or 16 bit numbers into memory. It would be messy to pack 9 bit numbers into memory, and also wasteful since we couldn’t use all 64 bits.

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