The system includes a low-pass filter that eliminates
 aliasing distortion  as described above. this filter becomes active
around 4 KHz and gradually begins to attenuate (cut off) the signal.
Generally, you cannot clearly hear frequencies higher than 7 KHz.
Therefore, you get the most complete frequency response in the frequency
range of 0 - 7 KHz. If you are making frequencies from 0 to 7 KHz, you
should select a sampling rate no less than 14 KHz, which corresponds to a
 sampling period  in the range 124 to 256.

At a  sampling period  around 320, you begin to lose the higher frequency
values between 0 KHz and 7 KHz, as shown in Table 5-6.


          Table 5-6: Sampling Rate and Frequency Relationship


                            Sampling    Sampling    Maximum Output
                             Period    Rate (KHz)   Frequency (KHz)
                            --------   ----------   ---------------
     Maximum sampling rate    124         29              7
     Minimum sampling rate    256         14              7
       for 7 KHz output
     Sampling rate too low    320         11              4
       for 7 KHz output


In A2000's with 2 layer motherboards and later A500 models there is a
control bit that allows the audio output to bypass the low pass filter.
This control bit is the same output bit of the  8520 cia  that controls
the brightness of the red "power" LED (CIA A $BFE001 - Bit 1: /LED).
Bypassing the filter allows for improved sound in some applications, but
an external filter with an appropriate cutoff frequency may be required.