SNR of ADAU1772 ADC
I measured analog in to analog out (ADC to DAC) and was getting ~82dB SNR.
Should I expect better?
Using the two files you guys sent me in the other thread, I tested the ADC to serial IO out as well as serial IO in to DAC out and the DAC out test got good numbers but the ADC did not do as well as I would expect.
I don't understand the signal routing possibilities very well. I'd like to try SNR on two configurations:
1) ADC audio in to serial IO out before the DSP core.
2) ADC audio in to serial IO out after the DSP core.
Doing so would tell me if the DSP core is playing a negative role in the results.
I think I read somewhere there is a register setting to bypass the DSP? I should test this too.
I am using AIN2,3 unbalanced inputs. Schematic has them going to outputs 0 and 1 direct.
Barry
hardware
adau1772
Integrated/Special Purpose A/D Converters
Audio CODECs
Hello Barry,
The SNR may be correct if you are just referencing from a 0dBV level instead of full scale. You just mentioned -82dB but no reference given.
In addition, you will need to apply a filter. In the datasheet we show the specs for an A-weighted and a 20-20kHz filter. The 20-20kHz filter is called an AES-17 filter. Your AP might not have that filter available.
I think what you are measuring is good. I would have to check it here to verify.
The DSP core will NOT change anything with the audio out of the ADC then going to the serial port or the DAC. Unless you have it programmed to make changes in gain or EQ etc. The core just picks up the data and passes it along. It will not truncate the audio unless you make changes in the program running in the core that does that. Like if you lower the gain by 24dB then raise it back up your will lose the bottom 4 LSB bits. So don't do that in the core. There is plenty of headroom to do any EQ or addition to signals and then bring them back down using a gain control or limiter to prevent the signal from clipping on the way out of the core heading to the serial port or DAC. Read the section about Signal Processing in the datasheet. It explains the data formats.
This page in the register controls tab is where you select the routing of the data. You can go through the core or around it using these register settings.
Dave T
.
This is our routing setup for Analog In-Out. Do you see something wrong with it? Signal level of AP set to 1.25Vrms - just before THD+N raises above .03%. It gets just over 78dB SNR. Your setup had some things different for digital serial, which this is not using - correct? Thus I have that disabled.
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