I am new to this area of technology, i have just started developing small embedded applications but i find it difficult to understand what PWM audio is and how it can be implemented with the SOM mounted on my custom board. I have seen it work on WiringPi but need help implementing it on this SOM.
I have tried reading through TRM and tried referencing different blogs and articles but this topic is discussed very little.
I am starting a project to test the audio performance on linux.
What I need to do is to play the audio on our websystem and check the audio quality (or just check it has audio output) on linux.
I am going to record the audio on linux with ffmpeg. Is there any other better choice?
I don't know how to (automation) check I recorded is what I played, as well as the quality of recorded audio.
I think what you need is PESQ (Perceptual Evaluation of Sound Quality). However I have not found anything which is open source/free and out of the box.
You can download the recommendation from here:
http://www.itu.int/rec/T-REC-P.862-200511-I!Amd2/en
Basically this is the reference implementation of PESQ.
Sevana has an audio quality analyser which is not an ITU standard, it is AQuA:
http://www.sevana.fi/aqua_wiki.php
It is available for linux but I think you have to pay for it.
You can also check the similarities for two audio files with cross-correlation, please refer to here:
https://dsp.stackexchange.com/questions/736/how-do-i-implement-cross-correlation-to-prove-two-audio-files-are-similar
I just learned that lot of people are using Matlab or Octave to generate the necessary data, for example:
http://bagustris.blogspot.ie/2011/11/calculate-time-lag-from-cross.html
I'm looking for some general way to get video stream from webcam in Linux and then process and show it in a window. The second part seems simple, but I don't know how to deal with the first one.
Is there some API, lib, docs, etc?.. Where to start?
I've done a little of this before, and you're right, the second part is the easy part. You should take a look at this post for some of the commonly used libraries.
Video capture on Linux?
I would also throw OpenCV on that list, since it helps with both the obtaining and the processing of video streams:
http://sourceforge.net/projects/opencvlibrary/
http://www.willowgarage.com/pages/software/opencv
Good luck!
I want to work on a project where I have to segment and classify online audiovisual data based on its audio content, i.e. different parts of the audio visual data will be segmented and classified as silence, music, speech, speech+background music, etc based on their audio content.
I am aware that I have to obtain the audio part from the audiovisual data and extract features like zero crossing, spectral peaks, etc. and find out segment boundaries in order to segment audio data.
But I'm lost in the beginning itself.
I do not know how to start off with the project. The output of the software are segments of audiovisual data under different categories like silence, speech, music, etc.
It will be really helpful if someone lets me know
Which programming language is convenient for this purpose?
What steps should i follow in order to develop this software?
I have no background in digital signal processing. It'll be really helpful if I get some guidance
I'd suggest to look into a multimedia framework such as GStreamer. It is crossplatform, but the easiest to get started on Linux where it originates from. It already comes with all kind of plugins to receve, demux and decode audio and video. It also has a couple of analyzers (such as level and spectrum analyzers for audio as well as voice activity detection). Those could be a good starting point for your experiments. Gstreamer itself is written in C, but applications can use the language bindings to python, perl, c#, c++, java, ...
I have recently started going through sound card drivers in Linux[ALSA].
Can a link or reference be suggested where I can get good basics of Audio like :
Sampling rate,bit size etc.
I want to know exactly how samples are stored in Audio files on a computer and reverse of this which is how samples(numbers) are played back.
The Audacity tutorial is a good place to start. Another introduction that covers similar ground. The PureData tutorial at flossmanuals is also a good starting point. Wikipedia is a good source once you have the basics down.
Audio is input into a computer via an analog-to-digital converter (ADC). Digital audio is output via a digital-to-analog converter (DAC).
Sample rate is the number of times per second at which the analog signal is measured and stored digitally. You can think of the sample rate as the time resolution of an audio signal. Bit size is the number of bits used to store each sample. You can think of it as analogous to the color depth of an image pixel.
David Cottle's SuperCollider book also has a great introduction to digital audio.
I was in the same situation, and certainly this kind of information is out there but you need to do some research first. This is what I have found:
Digital Audio processing is a branch of DSP (Digital Signal
Processing).
DSP is one of the most powerful technologies that will
shape science and engineering in the twenty-first century.
Revolutionary changes have already been made in a broad range of
fields: communications, medical imaging, radar & sonar, high fidelity
music reproduction, and oil prospecting, to name just a few. Each of
these areas has developed a deep DSP technology, with its own
algorithms, mathematics, and specialized techniques…
This quote was taken from a very helpful guide that covers every topic in depth called the “The Scientist and Engineer's Guide to
Digital Signal Processing”. And though you are not asking for DSP specifically there’s a chapter that covers all digital audio related topics with a very good explanation.
You can find it in the chapter 22 - Audio Processing, and covers all this topics:
Human Hearing: how the sound is perceived by our ears, this is the
basis of how then the sound is then generated artificially.
Timbre: explains the properties of sound, like loudness, pitch and
timbre.
Sound Quality vs. Data Rate: once you know the previous concepts
we start to translate it to the electronic side.
High Fidelity Audio: gives you a picture of how sound is then
processed digitally.
Companding: here you can find how sound is then processed and
compressed for telecommunications.
Speech Synthesis and Recognition: More processes applied to the
sound, like filters, synthesis, etc.
Nonlinear Audio Processing: this is more advanced but understandable,
for sound treatment and other topics.
It explains the basics of sound in the real world, in case you might want to take a look, and then it explains how the sound is processed in the computer including what you are asking for.
But there are other topics that can be found in wikipedia that are more specific, let’s say the “Digital audio” page that explains every detail of this topic, this site can be used as a reference for further research, just in the beginning you can find a few links to sample rate, sound waves, digital forms, standards, bit depth, telecommunications, etc. There are a few things you might need to study more, like the nyquist-shannon theorem, fourier transforms, complex numbers and so on, but this is only used in very specific and advanced topics that you might not review or use. But I mention it just in case you are interested. You can find information in both the DSP guide book and wikipedia although you need to study some math.
I’ve been using python to develop and study these subjects with code since it has a lot of useful libraries, like numpy, sound device, scipy, etc. And then you can start plating with sound. On youtube you can find lots of videos that also guide you on how to do this. I’ve found synthesis, filters, voice recognition, you can create wav files with just code, which is great. But also I’ve seen projects in C/C++, Javascript, and other languages, so it might help you to keep learning and coding fun things.
There are a few other references across the internet but you might need to know what you are looking for, this book and the wikipedia page would be the best starting points for me, since it gives you the basics and explains in depth every topic. Then depending on the goal you want to achieve you can then start looking for more information.