Re: FLASH: sound

[Marc Hoffman, Poison Dart Frog Media]

At 01:23 PM 5/21/2000 , you wrote:


>Hello:

>

>If someone knows something about sound, plese, help me to clarify this

>doubt

>

>What is the difference between sample rate and bit rate?

>I know that sample rate is the frequency of sampling of the sound that

>determines its quality (resolution) and defines in khz... bit rate

>apparently defines in bits or kbps but i don't know what it determines.


You are right about sample rate -- it's just the number of times per second 

(1 kHz - 1,000 cycles per second) that the sound is measured. What digital 

sound attempts to do is to record a sound wave as a series of numbers, each 

measuring the wave at a moment in time. The more measurements per second, 

the higher the fidelity, up to about 40kHz, beyond which there's probably 

not a difference discernible to the human ear. A common analogy is to 

imagine trying to draw a smoothly curved wave form on paper by using only 

dots. The closer the dots are to each other, the more the drawing resembles 

a smooth line rather than a series of disconnected dots. Think of sample 

rate as the horizontal spacing of the dots.


Bit rate has to do with the range of values used to record each of those 

measurements. Think of it as the vertical resolution of the dots in your 

drawing -- more values to choose from means the vertical spacing is tighter 

and smoother. Bit rate (known as bit depth in color theory) is the number 

of binary digits used to store a single value. A bit rate of 2 would give 

only four values to choose from for each measurement -- 0, 1, 2, or 3. 

Obviously this would not give you a lot of range to measure the sound. 

16-bit is the standard for CD quality. 8-bit is usually fine for music, 

especially in multimedia where users aren't usually expecting the same 

quality they hear playing a CD on a high-end stereo system. Depending on 

what type of compression is used, 5-bit can also be okay for music. Lower 

bit rates are usually good only for voice and sound effects that have lots 

of noise in them already.


Hope this helps.


Marc Hoffman


Poison Dart Frog Media

Flash portfolio: http://www.dartfrogmedia.com/portfolio



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