[LAU] Sample rate vs. SNR

[Len Ovens]

On Wed, January 23, 2013 8:17 am, Fons Adriaensen wrote:
> On Wed, Jan 23, 2013 at 06:52:12AM -0800, Len Ovens wrote:
>
>> Just looking through TI's ADCs 96k and up. Any on chip audio circuitry
>> (level controls etc.) seems to lower SNR (101 db typ.) which is no
>> surprise. But what I did find interesting is that even 96k and 192k
>> devices seem to optimized for 48k. So the spec of 112db SNR would be
>> true
>> for 48k, but by the time it gets to 96k that is down 3db (noise floor up
>> 3db) and at 192k... not even listed.
>>
>> So 192k is snake oil anyway, I'm not concerned, though I will say the
>> 192k
>> device has better performance at 48K, much smoother frequency response.
>
> Noise in 24-bit ADC is all thermal noise in the analog parts,
> not quantisation noise. If it is measured unweighted it increases
> by 3 dB if the bandwidth is doubled. But for 96 kHz, half of it
> is above 24 kHz, so the noise within the audio bandwidth remains
> just the same. There is no degradation.
>
> The specs should tell you how exactly the SNR is measured. If the
> A-weighted or 20 kHz BW noise increase at 96 at 192 kHz there is
> something fishy.

Unweighted in the specs. Thank you for pointing that out.

-- 
Len Ovens
www.OvenWerks.net