pcm

alsa声卡驱动分析总结 分析只列出部分重要代码，具体请参考 linux3.0 内核代码。 Alsa 架构整体来说十分复杂，但对于驱动移植来说我们仅仅只需要关心 ASOC 就足够了。 在学习 asoc 之前我们先了解一些专业术语： ASoC currently supportsthe three main Digital Audio Interfaces (DAI) found on SoC controllers and portable audio CODECs today, namelyAC97, I2S and PCM. ASoC 现在支持如今的SoC 控制器和便携 音频 解码器上的三个主要数字音频接口，即AC97 ，I2S，PCM（与pcm音频格式注意区分，前者是一种音频接口，后者是一种输入声卡的音频格式）。 AC97 AC97 ==== AC97 is a five wire interface commonly found on many PC soundcards. It is now also popular in many portable devices. This DAI has a reset line and time multiplexes its data on its SDATA_OUT (playback) and SDATA_IN

最近一直忙于Linux下ALSA音频驱动的开，作了一次专题讨论，现将部分内容贴出来大家分享一下。 内容提要 一、音频相关的基础知识 •二、Linux下音频驱动开发模型 •三、socxx+ WM8993驱动实例分析 •四、总结 • 五、 Question& Discussion 音频相关的基础知识 ---- 采样、量化 •1、采样频率 • 常用 32kHz、 44.1kHz、 48kHz。 •2、量化精度 • 指对采样数据分析的精度，精度越高，声音就越逼真。常用8位、16位、24位。 音频相关的基础知识 ---- 音频设备硬件接口 •PCM接口：由时钟脉冲BCLK，帧同步信号FS及接收数据DR和发送数据DX组成。（先发MSB，后LSB）。 •IIS接口：在一个称为LRCLK的信号机制中经过多路转换，将两路音频信号变成单一的数据队列。LRCLK为高时，左声道数据被传输。 • AC97接口：AC97不只是一种数据格式，还具有控制功能。数据帧以SYNC脉冲开始，包括12个20位时间段及16位tag段，共256个数据序列。 音频相关的基础知识 ---- 音频放大器 • A类放大器 拓扑结构使用一只晶体管作为直流（DC）电流源，能够提供扬声器需要的最大音频电流。 • B类放大器 拓扑结构没有DC偏置电流，所以功耗大大减少。 • AB类放大器 是A类放大器和B类放大器的组合折衷

碰到一个开发 板录音的项目，结合网上的资料，自己总结 了一篇 头文件 #ifndef __RECORD_H #define __RECORD_H #include <alsa/asoundlib.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <signal.h> #include "threadsafe_queue.h" typedef long long off64_t; typedef struct SNDPCMContainer { snd_pcm_t *handle; snd_output_t *log; snd_pcm_uframes_t chunk_size; snd_pcm_uframes_t buffer_size; snd_pcm_format_t format; uint16_t channels;//声道 size_t chunk_bytes; uint32_t sample_rate;//采样率 size_t bits_per_sample;//比特率 size_t bits_per

I have a project for Android reading a short[] array with PCM data from microphone Buffer for live analysis. I need to convert this functionality to iOS Swift. In Android it is very simple and looks like this.. import android.media.AudioFormat; import android.media.AudioRecord; ... AudioRecord recorder = new AudioRecord(MediaRecorder.AudioSource.DEFAULT, someSampleRate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, AudioRecord.getMinBufferSize(...)); recorder.startRecording(); later I read the buffer with recorder.read(data, offset, length); //data is short[] (That's what i'm

Starting from this question I was made to understand how to deinterleave the left and right channel of a 16 bit PCM data. My question now is, how will a 8 bit PCM be deinterleaved and "stretched" into a 16 bit value 16-bit PCM has basically the same data bits and additional bits on the least significant bit side to specify the value and add accuracy and detail. Then 8-bit PCM is typically unsigned value with a centerpoint of 0x80 , and 16-bit (also applicable to higher bitnesses) PCM is signed integer, so the conversion formula is: UINT8 sample8 = ...; INT16 sample16 = (INT16) (sample8 - 0x80)

I'm trying to dynamically generate a small MP4 audio+video file directly from my Android app. My original plan of attack: The user enters some basic song data (a chord progression, etc) and the app builds a MIDI file. The system builds chord diagrams for each chord, and using a MIDI reader it generates the animations frames array that is timed to the MIDI Convert the MIDI into a raw PCM audio data <-- this S.O. question is specific to this point Apply the raw audio to the animation frames - and encode the audio and video frames into an MP4 Provide the resulting MP4 video to the user with

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: Bad news, everyone! I try to use a microphone on my Raspberry Pi through PyAudio but without success. The microphone is connected to a USB sound card. The microphone works when I go through 'arecord' : pi@raspberrypi ~ $ arecord -D plughw:0,0 -f cd test2.wav Recording WAVE 'test2.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo However, when I do the test record.py in PyAudio, I got an error. The error is the same for all programs in Python that uses PyAudio : pi@raspberrypi /usr/src/pyaudio/test $ python record.py ALSA lib pcm.c