# Calculating Noise in a System Question

#### jaydnul

Joined Apr 2, 2015
155
Hello,

I have a few questions based on the diagram below:

1. If I were to look at the signal on the input of Circuit 1, it will have an SNR_in that is defined by the source that is providing the input signal. However, if i look at SNR_1, and Circuit 1 has a much lower bandwidth than the input source, then SNR_1 will be potentially better than SNR_in even with the noise Circuit 1 will contribute. So does the calculation of SNR_in have to use the bandwidth value of the slowest circuit in the system (even though if you probed that input net it would have a much physically higher noise since it hasnt passed through the low bandwidth circuit yet)?

2. If Circuit 2 has a lower bandwidth than Circuit 3, do i have to first calculate SNR_2 using the bandwidth value of Circuit 2, then do a second calculation using the bandwidth of Circuit 3 to see how much of the SNR_2 noise actually gets through? #### Audioguru again

Joined Oct 21, 2019
4,524
If the noise is audio then is it low frequency hum or is it high frequency hiss?
Instead of filtering out the low frequencies causing voices to sound like chipmunks and filtering out the high frequencies causing voices to be muffled, why not eliminate the noise instead?