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LOW SNR FFT

Started by Richard August 7, 2019
Hello,
I am processing an audio signal with CS4244 codec at 24 bits and 48kHz. Every 2048 samples the FFT is calculated and its amplitude.
Without input signal I get FFT values ​​close to 30dB. With maximum input values ​​(overflow) I get values ​​of 90dB, with a scale of 0 to 120dB.
Why not get a dynamic range of 100-110dB as is logical in a 24bit process?
Any ideas?
Thanks.
On 7.8.19 15:18, Richard wrote:
> Hello, > I am processing an audio signal with CS4244 codec at 24 bits and 48kHz. Every 2048 samples the FFT is calculated and its amplitude. > Without input signal I get FFT values ​​close to 30dB. With maximum input values ​​(overflow) I get values ​​of 90dB, with a scale of 0 to 120dB. > Why not get a dynamic range of 100-110dB as is logical in a 24bit process? > Any ideas? > Thanks. >
The number of codec bits says nothing of the purity of the analog audio signal coming to your codec. Are you sure that the no-signal is quiet enough? -- -TV
Hi, thanks for the answer.
Yes, I'm sure, because I hear the "clicks" the signal makes when it saturates 
and the codec says that there is overflow. I use the output of a frofessional mixer.
On Wednesday, August 7, 2019 at 11:03:33 AM UTC-4, Richard wrote:
> Hi, thanks for the answer. > Yes, I'm sure, because I hear the "clicks" the signal makes when it saturates > and the codec says that there is overflow. I use the output of a frofessional mixer.
If I understand it may not be noise in the front end/mixer, but rather noise interjected by the processing equipment. What quality is the 24 bit converter circuit? What do you get for noise with no input at all, i.e. a shorted input? Are you using an eval board for the CODEC or your own board? -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209