Raw audio

RAW Audio is an audio file format for storing uncompressed audio in raw form. Comparable to WAV or AIFF in size, RAW Audio file does not include any header information (sampling rate, bit depth, endian, or number of channels)

convert an mp3 to raw

Using

• ffmpeg: " A complete, cross-platform solution to record, convert and stream audio and video."
• Sox: the Swiss Army knife of sound processing programs

Find out the properties of the audio file with ffmpeg

ffmpeg -i file.mp3
sox -V file.wav

Sox has no handler for mp3 formate, hence you have need to convert from mp3 to wav, ffmpeg does it quickly and well

ffmpeg -i file.mp3 -acodec pcm_s16le -ar 44100 file.wav

• -acodec pcm_s16le: audio codec is PCM signed 16bit
• -ar 44100: audio rate 44.1kHz

Sox: display information on the wav file

sox -V file.wav

Sox: convert the wav file to raw

sox file.wav -b 16 -c 1 -r 44100 -t raw file.raw

• -b 16 bit-rate
• -c 1 number of channels
• -r 44100sampling rate
• -t rawtarget raw

play (sox): play back the raw file at same bit-rate and sample-rate

play -b 16 --endian little -e signed -r 44100 -c 1 Zong3.raw

• --endian little: "specify whether the byte-order of the audio data is, respectively, `little endian'... Endianness applies only to data encoded as floating-point, or as signed or unsigned integers of 16 or more bits. It is often necessary to specify one of these options for headerless files"
• -e signed encoding. Signed is commonly used with a 16 or 24 -bit encoding size.

Same thing but with aplay:

aplay -f S16_LE -c 1 -r 44100 Zong3.raw

• -f sample forma+bit rate+endian:
  • 8bit: S8 U8
  • 16bit: S16_LE S16_BE U16_LE U16_BE
  • 24bit: S24_LE S24_BE U24_LE U24_BE
  • 32bit: S32_LE S32_BE U32_LE U32_BE
• -c: channel number
• -r: sample rate. 4000 Hz is the minimum allowed by aplay. 44100Hz is the default sample rate for CDs

convert image to raw audio

copy the image to another file, with the extension raw

cp img.png  img.raw

play: use sox previously use command to play that audio

play -b 16 --endian big -e signed -r 44100 -c 1 img.raw 

• lowering the sampling rate -r will slow-down the playback

Save the result of playing the raw file into audio file with a head (wav)

sox -r 44100 -b 16 -c 1 -e signed img.raw img.wav

Notice that the same audio parameters need to be declared: sample-rate, bit-rate, channel number, encoding

play: without having to declare any parameters

play img.wav 

Links

• Raw Audio File Formats Information (at the Wayback Machine)
• SOX Conversions, Raw Files, Splitting And Merging Channels
• Audio Conversion Cheat Sheet
• [SoX] in the Cookbook