[sdiy] OTish - CDDA bandwidth

[Antti Huovilainen]

On Thu, 14 Dec 2006, Nicholas Gregorich wrote:

> Now we all know the sampling rate is 44.1kHz.  However, the material I have
> says that CDs are sampled at twice Nyquist.  They say since Nyquist is 2x,
> then twice Nyquist is 4x, so the analog signal to be sampled must be band
> limited to 11.025kHz.

Ok, just to set things right:
CD bandwidth = 0-20kHz
CD data rate = 44.1kHz*2*2 bytes = 176400 bytes/sec

The nyquist frequency is obviously 22.05 kHz.
In practise the oversampling filter transition bandwidth is either 20-22 
kHz or 20-24 kHz.

And to avoid confusion when you run into sites that claim that sine at 15 
kHz cannot be represented properly by such "low" samplerate, CD (and all 
digital audio) playback assumes a reconstruction filter which smoothes the 
waveform and removes the aliases. In practise this is done by a 
combination of digital oversampling (often 8x) and low order analog 
lowpass filter after the DAC.

Antti

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