Hi Expert:
We test our DM368 voice codec output frequency. Use the same voice player software and set the Gain to 0dB.
Test 300Hz to 7KHz sine wave. Find that the speaker out Pin-B9 the Vpp value is different. Pin-B9 external component has been removed. I think the frequency vs voltage affect by the low pass filter.
How can we disable the voice codec? We want the output Vpp different is small below 8KHz.
Thanks!
| Number | frequency（Hz） | Output（PK-PK）（V） |
| 1 | 300 | 2.87 |
| 2 | 500 | 2.85 |
| 3 | 1000 | 2.8375 |
| 4 | 3000 | 2.725 |
| 5 | 4000 | 2.6375 |
| 6 | 5000 | 2.5875 |
| 7 | 6000 | 2.41 |
| 8 | 7000 | 2.375 |
(sprufi9b.pdf)
1.2.3 D/A Convertor (DAC)
The DAC includes a single-bit DSM interpolation filter and switched capacitor reconstruction low-pass filter
(SC LPF). These can be used to obtain high PSRR, low jitter sensitivity, and low out-of-band noise.