this is awesome.
How can i get such a board ?
Thank you very much sir! Well, you get one from me when it's finished
I'm working on integrating the usb audio board with the amp. The amp used in the vid is about 200 USD which is far too expensive. The final Frankencat would probably be something like 60 USD including PCB(s) and all the parts as a self assembly kit.
I send the food for your cat. Two flavours.
Thanks, I got them and they both play well. I'll make a vid of the smaller one (really nice btw) but it won't tell you much since the sound quality will be limited to that of the iPhone/Youtube-combination, which is poor to say the least.
What I can tell you is that, while a 256kbps mp3 means good quality sound (256 * 1.024 = 262.144 bits per second), it's not much in comparison to the 16bit@48kHz = 2 * 16 * 48.000 = 1.536.000 bits per second (DVD quality) that the Frankencat is theoretically capable of. You can of course play even better stuff on your PC but it would be transcoded into 16bit@48kHz.
The Mp3 music format uses a trick to manage destructive compression (i.e. compression that doesn't result in an exact copy after decompression) with relatively low loss in common user experience. The trick is based on things specific to the function of the human ear which allows the algorithm to skip certain details that most of us can't hear anyway. This and the fact that mp3 normally has a lower bit rate on parts of the song that doesn't drastically change over time while the bit rate increases when the is a lot of variance or energy in the song.
So given a maximum bit rate of 256kbps, the algorithm uses a relatively lower compression ratio on low-variance parts and a higher compression ratio on high-variance parts up to a maximum of 256kbps. I believe this is called variant bit rate
(VBR) and there's also something called CBR meaning constant bit rate
where bit rate is constant at all times during the song.
I think that the 256kbps file you sent is a VBR, meaning that the maximum bit rate can be 262.144 bits per second.
Question, what do you think about the idea to extend it to have it fed by some air play through wifi or xbee or .... ? Just to make a wireless speaker for example, just to put it out on my terrace plug it into some power and stream from pretty much any source available ...
Personally, I think it's a wonderful idea and I've actually been thinking in that direction too, but it would fit better in old sleeping project of mine:
The device in that project operates completely on itself and does not require a PC but plays mp3, Flac, Ogg Vorbis and WAV files stored on SD card. Add a WLAN module, implement Air Play on the mini and fit it all together with an amp inside a speaker!
It's based on a chip that is capable of 16bit@192kHz audio which would yield 6.144.000 bits per second. However, due to the speed limitations of the Netduino (and poor availability of higher bit rate mp3s), I've only managed to play 320kbps mp3 CBR on it. I could probably push it higher but I don't have that kind of files. As most of us don't, the higher speed is of little practical use in my opinion.
There are formats around to allow for 48bit@384kHz or maybe even "better" but I think those are way beyond human perception and mainly used by professionals for studio master recordings and such.
EDIT: I'm not sure that what I write here is a 100% accurate but let's say 90% so you maybe want to look it up on Wikipedia.