ADAU1701 Filter Latency
hi guys
I need your help. I designed a digital filter by Matlab and load the transform function parameters into the ADAU1701 board.The curve simulated in sigma studio is right，but I test the board use a spectral analysis SW and the phase shift.
The first figure is simulated by sigmastudio and the second one is test by spectral analysis SW.
Is the phase shift due to the latency of the board,which is between the ADC and the DAC? How can I solve this problem and get a good curve.Thanks for your help.
Audio Signal Processors
digital filter
adau_1701
latency
SigmaDSP Audio Processors
adau 1701
adau1701
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Hello,
The phase lag you're experiencing occurs within the ADAU1701's converters themselves. The ADC includes an anti-aliasing filter, the DAC has a reconstruction filter. Both are digital filters which impose a total delay of just over 1 mS at the standard 48 KHz sample rate. In turn, this adds a frequency-dependent phase lag of:
phase in degrees = 360 x Tdelay x f Example: T = 1.08 mS, f = 1 KHz, then phase lag = 390 degrees. This directly adds to your filter's phase shift.
To accurately measure your filter's phase lag, you could add a second signal path from input directly to another DAC without filtering, to use as a reference. Have your analyzer measure the difference in phase between the two paths.
On the other hand, if your application requires near zero analog-in to analog-out latency in real time, the ADAU1701 won't work for you. See if the ADAU1772 is suitable -- it features a converter in-out lag of 38 uS, but offers only limited functions. This chip finds use in noise-cancelling headphones.
Best regards,
Bob
Hello,
If you need even less latency we are coming out with a newer version of the 1772 with even less latency. The processor in the 1772, and this new part, are simply filter engines so if most of what you need to do is implement a bi-quad filter then this part would most likely work well for you. Contact me if you need more info.
Dave T
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