pmc Posted July 19, 2015 Report Share Posted July 19, 2015 To go FPGA or external dedicated DAC is the question I'm asking myself right now. I'd rather go FPGA. I haven't taken a close look at Magnus's Wave-file player yethttp://forum.gadgetfactory.net/index.php?/topic/1775-wave-file-player-using-sigma-delta-dac/but the two songs demonstrating his sigma-delta DAC implementation sound really impressive. @asic_designer, how does it sound now ? have you got CD quality ? Quote Link to comment Share on other sites More sharing options...
mkarlsson Posted July 19, 2015 Report Share Posted July 19, 2015 Hi, after experimenting with several on-board DAC variants, I think it is very unlikely that you'll get anywhere near CD qualityAs a test signal, find a single-note piano sample and listen as it decays into the noise floor. If your experience is like mine, you'll hear dirty crunch-and-grind noises when the level gets too low.Subjectively, I'd give it 10 effective bits and that's it. There are a number of decent I2C DAC modules boards out there. An on-board DAC is nice for debugging but won't cut it for any serious project. I did look around for a short piano sample and found one that I think is a good test.It's available here: http://www.saanlima.com/download/pipistrello-v2.0/piano.wav To play this short sound clip on pipistrello using the waveplayer example, just copy it to the root of an sd-card and us it with the waveplayer bit file.When I ran it on my speakers (Dell amplified PC speakers) I could not hear any difference between playing it using the PC and using the Pipistrello board.This sample is 16-bit stereo at 44.1 KHz and the waveplayer is doing 12-bit DACs using a 120 MHz clock. It would be interesting to hear what other people think about the sound quality. Magnus Quote Link to comment Share on other sites More sharing options...
asic_designer Posted July 19, 2015 Author Report Share Posted July 19, 2015 To go FPGA or external dedicated DAC is the question I'm asking myself right now. I'd rather go FPGA. I haven't taken a close look at Magnus's Wave-file player yethttp://forum.gadgetfactory.net/index.php?/topic/1775-wave-file-player-using-sigma-delta-dac/but the two songs demonstrating his sigma-delta DAC implementation sound really impressive. @asic_designer, how does it sound now ? have you got CD quality ? Hi In all honesty I can't tell the difference. My girlfriend had been listening to me trying different fixes for this DAC issue for almost 3 or 4 days, and once I applied the fix, and she heard the music, she asked me, "so you gave up on trying to fix your circuit problem, I see you went back to playing music through your iPad." LMAO, she didn't even realize that I was playing the music through the FPGA. I still haven't told her LOL. So you might be able to tell the difference using an oscilloscope, but I can't hear the difference, its sounds great to me, and my girlfriend! Quote Link to comment Share on other sites More sharing options...
pmc Posted July 20, 2015 Report Share Posted July 20, 2015 Thanks for the feedback, much appreciated. Sounds very promising, I'll try it and report my results. Quote Link to comment Share on other sites More sharing options...
offroad Posted July 20, 2015 Report Share Posted July 20, 2015 I did look around for a short piano sample and found one that I think is a good test.It's available here: http://www.saanlima.com/download/pipistrello-v2.0/piano.wav Hi, should do as an example. The interesting part is the last second, it does drop to about 1 bit level.Of course, we have to crank up the volume so that the signal is still audible. In general, it is impossible to judge audio quality reliably by casual listening. For example, the gain setting needs to be very high so that the artifacts we are interested in are still above hearing threshold.I could argue whether I need that for everyday use (how did we ever manage with compact cassettes and FM radio), but then I'm compromising "CD quality". Quote Link to comment Share on other sites More sharing options...
pmc Posted July 24, 2015 Report Share Posted July 24, 2015 A lot can be improved in my setup but here are some preliminary results: setup:CD audio data: 16-bit Fs = 44100 (128Fs external oscillator connected to the FPGA)SDM clock = 200MHzSDM RC low-pass filter = 3.2K * 4300pF (Fc=11.5KHz)FPGA outputs = LVTTL 24mA image #1the yellow trace is from a soundcard output (@5512.5Hz), the green trace is the sigma-delta output-> above ~5/6KHz a sinewave just looks worse and worse as frequency increases image #2fft analysis of the sigma-delta output (@5512.5Hz) image #3frequency analysis when feeding the DAC with a sinesweep and the output is connected to a soundcard ADC listening testattached:- before.wav = the original audio data (mezzo-soprano)- after.wav = sigma-delta DAC then back to digital with PC soundcard ADC (Digigram VXpocket) Using standard headphones on a PC I couldn't hear any differences but in a multi-amps setup the difference was clear: pristine sound quality and better dynamic range with the original audio data preliminary conclusionthe sigma-delta audio quality is pretty good for an amazingly simple implementation (Xilinx xapp154 is a must-read I think) before.wavafter.wav Quote Link to comment Share on other sites More sharing options...
Jack Gassett Posted July 24, 2015 Report Share Posted July 24, 2015 PMC, Thank you very much for putting this analysis together. It is very interesting to see some concrete evidence of the output quality. Now the question is if anything can be tweaked to make the sound better? Thanks,Jack. Quote Link to comment Share on other sites More sharing options...
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