Can the total decimation factor be changed ?

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宇航号
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Joined: Mon Mar 12, 2018 8:30 am

Can the total decimation factor be changed ?

Postby 宇航号 » Tue Apr 23, 2019 2:43 pm

Hi, all
According the lib_mic_array-[userguide](3.0.1rc1),
1、48kHz, 24kHz, 16kHz, 12kHz and 8kHz output sample rate by default (3.072MHz PDM clock);
2、44.1kHz, 22.05kHz, 14.7kHz, 11.025kHz and 7.35kHz output sample rate by default (2.8224MHz PDM clock)。
The PDM to PCM conversion is divided into three stages,In each stage,the decimation factor is different:
in the first stage,the decimation factor is 8;
in the second stage,the decimation factor is 4;
in the third stage,the decimation factor is n ,which can be on of the 2,4,6,8,12。
So,the total decimation factor will be( 8 * 4 * n),It's always greater than 32.

But,I need a total decimation factor of 32 or 16.

Can I do something to change the decimation factor of second satge from 4 to 1 ?
So,the total decimation factor can be (8 * 1 * n),when n is equal to 2 or 4, I get 32 or 16.

Can I do this just change the filter coefficient of the second stage :
const int g_second_stage_fir[8] = {
0xffc7155a,
0x0020f817,
0x01fedc78,
0x0688d589,
0x0ee359f7,
0x19a643bc,
0x23fe05a0,
0x2a96c7ea,
};

Thanks a lot !

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