{"id":5996,"date":"2023-11-25T15:59:29","date_gmt":"2023-11-25T14:59:29","guid":{"rendered":"https:\/\/www.pschatzmann.ch\/home\/?p=5996"},"modified":"2024-03-21T07:50:38","modified_gmt":"2024-03-21T06:50:38","slug":"arduino-audio-tools-communication-with-serial","status":"publish","type":"post","link":"https:\/\/www.pschatzmann.ch\/home\/2023\/11\/25\/arduino-audio-tools-communication-with-serial\/","title":{"rendered":"Arduino Audio Tools: Audio over Serial"},"content":{"rendered":"

So far I have always preferred to send audio using the networking functionality<\/strong> of the micro-controllers. This is usually fast and reliable<\/strong>. Many examples can be found in my communications examples folder<\/a> using different protocols.<\/p>\n

Using Wires<\/h2>\n

But we can also send audio signals over a physical wire. I prefer to use the Serial protocol<\/strong> because this is well supported across all environments.<\/p>\n

Just to proof the case I had a simple demo<\/a> which was sending some some audio via the Serial TX pin and receives them back on the RX pin in order to play it back<\/p>\n

Serial Communication gets unreliable at high bit rates<\/strong> and it can happen that a single byte can get lost. This has the consequence that some nice audio is turning suddenly into noise<\/strong>! A usual sample rate is 44100 samples per second. If we use stereo with 16 bit we will need a baud rate of >= 1587600 which is well above the reliable range!<\/p>\n

Using 8 bit Samples<\/h2>\n

When we use 8 bit samples instead of 16 bits we not only can half the needed baud rate, but we also solve the issue of the lost bytes: If some bytes get lost, this will not be audible. The consequence is only that the channels get switched. In our framework we can use a codec to translate between the 8 and 16 bits. The minimum baud rate for 44100 samples stereo is 793800.<\/p>\n

Here is the new example<\/a> that uses 8 bits.<\/p>\n

This is by far my preferred solution<\/strong>: It is technically very simple and efficient<\/strong>!<\/p>\n

Using A Codec – E.g. ADPCM<\/h2>\n

ADPCM is an efficient codec that we can use on micrcontrollers and that provides a compression ratio of 1:4. But here as well, any lost bytes will lead to decoding errors. I noticed in my tests that a baud rate up to 115200 is usually very reliable.<\/p>\n

I added some container functionality that can provide next to the audio segments<\/strong> also meta data<\/strong> and other information. The audio information is checked with a checksum<\/strong> and invalid segments are discarded.<\/p>\n

Here is the related example<\/a> that can handle stereo with 44100 samples \/ second<\/strong>.<\/p>\n

Dependencies<\/h2>\n