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Re: "Bit width" vs "bit depth"
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Re: "Bit width" vs "bit depth"


  • Subject: Re: "Bit width" vs "bit depth"
  • From: Stephen Davis <email@hidden>
  • Date: Thu, 21 Jun 2007 00:01:31 -0700

On Jun 20, 2007, at 10:45 PM, Andy Peters wrote:

Maybe somebody here can explain.

The System Profiler tells me that my Mac mini's built-in audio supports two formats: PCM 16 and PCM 24.

What's interesting is that for each, we're told that there's both a Bit Depth and a Bit Width. For PCM 16, both of these are 16, and for PCM 24, the Depth is 24 and the Width is 32.

My question: WTF? How can it be both "wide" and "deep"?

For the "depth = 24, width = 32" case, this means there are 24 bits of resolution for the audio data BUT the 24 bits are arranged in memory as 32-bit words, mostly to make things more efficient for a variety of operations. For example, packing the samples in this fashion makes the conversion to other formats (e.g. floats) more efficient: accessing 3-byte "words" is inefficient for any processor so expanding the 3 bytes into a 4-byte "word" helps immensely. While 24-bit resolution is great for audio quality, it's kinda sucky in other respects. :-)


hth,
stephen
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References: 
 >"Bit width" vs "bit depth" (From: Andy Peters <email@hidden>)

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