本文基于觸覺智能RK3506核心板/開發(fā)板，介紹DSM音頻功能使用攻略。

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DSM簡介

DSM

DSM（Delta-Sigma Modulation，德爾塔-西格瑪調(diào)制）音頻原理，DSM 的核心是一種過采樣噪聲整形技術(shù)，它的目標(biāo)不是一次性精確地記錄每個(gè)采樣點(diǎn)的幅度，而是通過極高的采樣率來記錄相鄰采樣點(diǎn)之間的變化（Delta, Δ），并將量化誤差（噪聲）推擠（Sigma, Σ, 意為求和與積累） 到人耳不敏感的高頻區(qū)域，再通過數(shù)字濾波器將其濾除。

DSM應(yīng)用

以ADC為例，負(fù)責(zé)將麥克風(fēng)、樂器等模擬音頻信號(hào)轉(zhuǎn)換為數(shù)字信號(hào)，DSM 技術(shù)在此場景中解決了 “高精度與低成本” 的矛盾 —— 傳統(tǒng)多位數(shù) ADC（如 16 位、24 位）依賴復(fù)雜的模擬電路來保證精度，而 DSM ADC 通過 1 位量化器 + 過采樣 / 噪聲整形，用數(shù)字算法替代部分模擬電路成本，同時(shí)實(shí)現(xiàn)更高動(dòng)態(tài)范圍。像汽車音頻：車載麥克風(fēng)（用于語音助手、降噪通話）。汽車環(huán)境存在發(fā)動(dòng)機(jī)、風(fēng)噪等干擾，DSM 的噪聲整形技術(shù)可將量化噪聲推至人耳不敏感的高頻段（>20kHz），提升語音信號(hào)的信噪比。

硬件連接參考

硬件修改

觸覺智能RK3506開發(fā)板由于默認(rèn)使用ES8388音頻編解碼芯片，需整改硬件，修改如下：空貼R183、R174，焊接R180、R178。

內(nèi)核配置

打補(bǔ)丁

將觸覺智能提供的RK3506網(wǎng)盤中，軟件資料/Linux/patch/dsm路徑下的文件替換/kernel/sound/soc/codecs/下的文件。

DTS配置

相關(guān)配置如下，需要注意以下2點(diǎn)：

1.RK3506 sndcpu必須為sai3。

dsm_sound: dsm-sound { status = "okay"; compatible = "simple-audio-card"; simple-audio-card,format = "i2s"; simple-audio-card,mclk-fs = <256>; simple-audio-card,name = "rockchip,dsm-sound"; simple-audio-card,bitclock-master = <&sndcodec>; simple-audio-card,frame-master = <&sndcodec>; sndcpu: simple-audio-card,cpu { sound-dai = <&sai3>; }; sndcodec: simple-audio-card,codec { sound-dai = <&acdcdig_dsm>; }; }; &acdcdig_dsm { status = "okay"; }; &sai3 { status = "okay"; }; &audio_codec { status = "okay"; };

2.觸覺智能RK3506開發(fā)板(EVB3506)的es8388聲卡與DSM復(fù)用，所以配置DSM功能前需先關(guān)閉es8388相關(guān)配置。

es8388_sound: es8388-sound { status = "disabled"; compatible = "rockchip,multicodecs-card"; rockchip,card-name = "rockchip-es8388"; spk-con-gpio = <&gpio0 RK_PB6 GPIO_ACTIVE_HIGH>; rockchip,pre-power-on-delay-ms = <30>; rockchip,post-power-down-delay-ms = <40>; rockchip,format = "i2s"; rockchip,mclk-fs = <256>; rockchip,cpu = <&sai1>; rockchip,codec = <&es8388>; rockchip,audio-routing = "Headphone", "LOUT1", "Headphone", "ROUT1", "Speaker", "LOUT2", "Speaker", "ROUT2", "Headphone", "Headphone Power", "Headphone", "Headphone Power", "Speaker", "Speaker Power", "Speaker", "Speaker Power", "RINPUT1", "Main Mic", "RINPUT2", "Main Mic", "LINPUT1", "Headset Mic", "LINPUT2", "Headset Mic"; pinctrl-names = "default"; pinctrl-0 = <&spk_ctrl>; }; &i2c0 { status = "okay"; pinctrl-names = "default"; pinctrl-0 = <&rm_io0_i2c0_scl &rm_io1_i2c0_sda>; es8388: es8388@11 { status = "disabled"; #sound -dai-cells = <0>; compatible = "everest,es8388", "everest,es8323"; reg = <0x11>; clocks = <&mclkout_sai1>; clock-names = "mclk"; assigned-clocks = <&mclkout_sai1>; assigned-clock-rates = <12288000>; pinctrl-names = "default"; pinctrl-0 = <&rm_io8_sai1_mclk>; }; };

播放音頻測試方法

查看DSM聲卡，命令如下：

root@rk3506-buildroot:/# aplay -l **** List of PLAYBACK Hardware Devices **** card 1: rockchipdsmsoun [rockchip,dsm-sound], device 0: ff4a0000.sai-rk_dsm rk_dsm-0 [ff4a0000.sai-rk_dsm rk_dsm-0] Subdevices: 1/1 Subdevice #0 : subdevice #0 root@rk3506-buildroot:/#

配置功放芯片，將功放芯片開關(guān)腳拉高，命令如下：

root@rk3506-buildroot:/root# echo 14 > /sys/class/gpio/export root@rk3506-buildroot:/root# echo out > /sys/class/gpio/gpio14/direction root@rk3506-buildroot:/root# echo 255 > /sys/class/gpio/gpio14/value

使用aplay播放音頻，命令如下：

root@rk3506-buildroot:/# aplay -Dhw:1,0 1KHZ.wav Playing WAVE '1KHZ.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo

當(dāng)播放1k頻率音頻文件，示波器抓取經(jīng)過RC濾波前后的音頻信號(hào)如下:

RC濾波前的信號(hào)為放大查看：

RC濾波后的音頻信號(hào)查看：

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