Hello Shiggy-san,
I tried to download your LZH file, but I could not open it in my zip
program. It complains about invalid file headers, so maybe my
download was bad. (My zip program is supposed to handle LZH files
too.)
So I looked at TI's datasheet for the PCM2906. Apparently, this IC
includes built-in low-pass filters for the DAC and ADC.
The PASS_BAND is the range of frequencies below half the sampling
rate, where the frequency response should be relatively flat.
The STOP_BAND is frequencies much higher than half the sampling rate,
where there should be a larger attenuation.
In those graphs from the TI datasheet, they are just scaling the
amplitude and frequency ranges (Y and X axes) to look at those
portions of the frequency response curve. For the PASS_BAND plot,
they are looking at frequencies below half the sampling rate (Nyquist
limit). For the STOP_BAND plot, they are looking more at higher
frequencies, to see the larger attenuation there.
I THINK that is what the curves are SUPPOSED to be showing. But those
particular curves do not seem to be consistent with one another.
Figure 23 shows the response is -1dB at about 80 kHz ... but on Figure
22 it is about -6dB at the same frequency, and the -1dB point looks
like it is below 20 kHz. That might just be an error in preparing
those figures in the datasheet (yes, mistakes like that do happen).
Regards,
Andy
