Why there are so many bits in sigma-delta audio codec?

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ruwan2

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Hi,

Many audio codec uses sigma-delta technology. I do not understand why there are so many bits, which are far more than the SNR spec. For example, ADI has ADAU1761 which is 24-bit, 98 dB SNR. I don't think 98 dB SNR needs 24 bit.
Could you tell me that?

Thanks.
 

For ideal ADC SNR=6.02*N+1.76 dB
It is true that for 24 bit SNR should be much greater than it actually is. But there are a lot of noise sources in real applications so this ideal parameter could not be achieved.
For example, 1 LSB for 24 bit and 3.3 VREF = 0.2 uV. Do you have such a stable power source?

Try to read Walt Kester "Analog-digital Conversion", chapter 2.3
 

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