FM stereo generator Bug with SigmaStudio 3.3
Hi,
I need to create a FM stereo generator with adau1701, the application
https://ez.analog.com/message/7959#7959, a have of the BUG in SIGMADSP software.
With 19khz doubler of the frequency is 38khz.
1KHZ sine wave only L or only R 0dB in ADC
When the output is sent to the DAC, the sine wave frequency 38khz is ok, but
when we apply this signal in a multiplier with the L - R to generate the
modulated DSB-SC subcarrier, the signal is only half.
When the signal generator is applied directly to the multiplier with the 38khz
signal is perfect DSB-SC. When applied to the doubler with 19 kHz signal is
generated the problem.
My problem is of the phase with 38khz and 19khz.
Is there any way to divide the frequency of 38khz by 2??
Best Regards,
Fabio Moura
Audio Signal Processors
SigmaDSP Audio Processors
adau1701
Thanks very much for your help, MagicRub! That's the correct solution to the problem.
I included some scope shots here.
Original project (no multiplication):
Project including multiplication...modulated signal only appears above or below the zero line:
Adding the DC blocking filter in SigmaStudio:
Resulting output is correct:
(Note: I ran these tests at 48 kHz, but the results at 192 kHz should be the same)
Thank you very much!!!
Thank you very much!!!
When you multiply two AC signals you get the difference and the sum. In the case of multiplying a signal by it's self you get double and 0. Zero Hz is DC so you have an offset which is throwing you off. Put it through a DC block or a super low HPF (10 Hz?) and you should be fine.
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