使用stm32的ADC采集音频数据然后实时用DAC播放。采样频率为16000，缓冲区为1024，设计一个移频滤波算法，用来防止声音反馈

移频滤波算法可以通过将音频信号乘以一个正弦函数来实现，即：

y(n) = x(n) * cos(2πf*Ts*n)

其中，y(n)为滤波后的信号，x(n)为采集到的原始音频信号，f为移频的频率，Ts为采样时间间隔，n为采样点数。

具体实现步骤如下：

1. 初始化ADC和DAC，设置采样频率为16000，缓冲区大小为1024。

2. 定义一个正弦函数，用于进行移频滤波。

3. 循环读取ADC采集到的音频数据，并将其乘以正弦函数，得到滤波后的音频数据。

4. 将滤波后的音频数据写入DAC缓冲区，并实时播放。

5. 重复步骤3和步骤4，实现实时移频滤波播放。

代码示例：

#include "stm32f4xx.h"

#define SAMPLE_RATE 16000
#define BUFFER_SIZE 1024

uint16_t adc_buffer[BUFFER_SIZE];
uint16_t dac_buffer[BUFFER_SIZE];

float sin_table[BUFFER_SIZE];

void init_sin_table(void)
{
    float f = 1000.0;
    float Ts = 1.0 / SAMPLE_RATE;
    float w = 2.0 * 3.1415926 * f * Ts;
    int i;
    for(i = 0; i < BUFFER_SIZE; i++)
    {
        sin_table[i] = cos(w * i);
    }
}

void init_adc(void)
{
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    GPIO_InitTypeDef gpio;
    gpio.GPIO_Mode = GPIO_Mode_AN;
    gpio.GPIO_Pin = GPIO_Pin_0;
    gpio.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOA, &gpio);

    ADC_InitTypeDef adc;
    adc.ADC_ContinuousConvMode = ENABLE;
    adc.ADC_DataAlign = ADC_DataAlign_Right;
    adc.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;
    adc.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_Rising;
    adc.ADC_NbrOfConversion = 1;
    adc.ADC_Resolution = ADC_Resolution_12b;
    ADC_Init(ADC1, &adc);

    ADC_RegularChannelConfig(ADC1, ADC_Channel_0, 1, ADC_SampleTime_3Cycles);

    ADC_Cmd(ADC1, ENABLE);
}

void init_dac(void)
{
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    GPIO_InitTypeDef gpio;
    gpio.GPIO_Mode = GPIO_Mode_AN;
    gpio.GPIO_Pin = GPIO_Pin_4;
    gpio.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOA, &gpio);

    DAC_InitTypeDef dac;
    dac.DAC_Trigger = DAC_Trigger_T2_TRGO;
    dac.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
    DAC_Init(DAC_Channel_1, &dac);

    DAC_Cmd(DAC_Channel_1, ENABLE);
    DAC_DMACmd(DAC_Channel_1, ENABLE);
}

void init_timer(void)
{
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    TIM_TimeBaseInitTypeDef tim;
    tim.TIM_Prescaler = 0;
    tim.TIM_CounterMode = TIM_CounterMode_Up;
    tim.TIM_Period = 84 - 1;
    tim.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInit(TIM2, &tim);

    TIM_OCInitTypeDef oc;
    oc.TIM_OCMode = TIM_OCMode_PWM1;
    oc.TIM_OutputState = TIM_OutputState_Enable;
    oc.TIM_Pulse = 42 - 1;
    oc.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM2, &oc);

    TIM_Cmd(TIM2, ENABLE);
}

void init_dma(void)
{
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA1, ENABLE);

    DMA_InitTypeDef dma;
    dma.DMA_Channel = DMA_Channel_7;
    dma.DMA_PeripheralBaseAddr = (uint32_t)&DAC->DHR12R1;
    dma.DMA_Memory0BaseAddr = (uint32_t)dac_buffer;
    dma.DMA_DIR = DMA_DIR_MemoryToPeripheral;
    dma.DMA_BufferSize = BUFFER_SIZE;
    dma.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    dma.DMA_MemoryInc = DMA_MemoryInc_Enable;
    dma.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
    dma.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
    dma.DMA_Mode = DMA_Mode_Circular;
    dma.DMA_Priority = DMA_Priority_High;
    dma.DMA_FIFOMode = DMA_FIFOMode_Disable;
    dma.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
    dma.DMA_MemoryBurst = DMA_MemoryBurst_Single;
    dma.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
    DMA_Init(DMA1_Stream5, &dma);

    DMA_Cmd(DMA1_Stream5, ENABLE);
}

int main(void)
{
    init_sin_table();
    init_adc();
    init_dac();
    init_timer();
    init_dma();

    while(1)
    {
        int i;
        for(i = 0; i < BUFFER_SIZE; i++)
        {
            adc_buffer[i] = ADC_GetConversionValue(ADC1);
        }

        for(i = 0; i < BUFFER_SIZE; i++)
        {
            dac_buffer[i] = adc_buffer[i] * sin_table[i];
        }
    }
}