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 Forum index » DIY Hardware and Software » Microcontrollers and Programmable Logic
SK-Synth: A subtractive FPGA synthesizer
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BOB-SNARE



Joined: Sep 26, 2008
Posts: 30
Location: Australia

PostPosted: Sun Oct 03, 2010 9:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

What's your sampling rate?
Did you worry about band-limited waveforms for the DCOs?
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stekern



Joined: Aug 06, 2010
Posts: 14
Location: Finland
Audio files: 5

PostPosted: Mon Oct 04, 2010 5:03 am    Post subject: Reply with quote  Mark this post and the followings unread

The final sampling rate is determined by the I2S chip, and it is limited 50kHz in my case.
Inside the synth it is the filters sampling rate that is the limiting factor and it is 96kHz.

The waveforms have not been band-limited so far,
but I have reworked the oscillators to read the waveforms from the flash-memory on the avnet devboard (instead of partly generating them in the FPGA),
which will make it alot easier to implement band-limited waveforms.
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AudioCity_Music



Joined: Sep 25, 2012
Posts: 2
Location: Bristol, UK

PostPosted: Wed Sep 26, 2012 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Don't know if anyone of you lads check this forum anymore, but might as well give it a try.
Hi all,
My name is Pete and I'm a Computer Systems Integration student from the University of the West of England.
I'm attempting to use your code in my final year project, I hope you don't mind. Interestingly, I also have to port your design onto an Altera board.

I have a few questions here:
1) I noticed there's a DCM block, which I assume comes from Xilinx libraries. Could you tell me what frequency clk/clkfx is supposed to run? Is it just one global clock, or do the cores (synth, flash_mux, i2s etc.) need different clock frequencies to run correctly?
2) what's the purpose of flash_mux, ac'97 and i2c and SK_Drums? I can't see any waveform signal ever going into ac'97, which I thought was the DAC for audio output?

Thank you in advance for any help.
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stekern



Joined: Aug 06, 2010
Posts: 14
Location: Finland
Audio files: 5

PostPosted: Wed Sep 26, 2012 6:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

First, I don't mind at all, I'm just happy if someone finds it useful. Wink
Porting to altera shouldn't be too much trouble, I believe the DCM is about
the only non-generic code in the project.

1) That's there to multiple the boards 16 MHz clock to (IIRC) 48 MHz.
There is only one global clock, so it is only necessary to generate that.

2)
- SK_Drums is a small "drum-machine.
All it does is that it play (drum) samples straight from the parallell flash on the avnet board.

- flash_mux is an arbiter between SK_Drums and the waveform to the flash memory.
You don't need to have a parallell flash to use the synth, only without, SK_Drums will not function and the number of waveforms will be limited.

- I2S and AC97 are used to transform the output from the synth to the DAC, I've used the synth on 2 boards, avnet devboard - has I2S and atlys - has AC97.
You choose one of them (or implement your own, if neither suits. What board are you going to use?)
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AudioCity_Music



Joined: Sep 25, 2012
Posts: 2
Location: Bristol, UK

PostPosted: Thu Sep 27, 2012 12:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks SK for your prompt reply.
Incidentally, I don't know about you but I'm not an electronic engineer, so my questions might seem a bit silly at times Laughing
At uni I'm doing a mixture of software/hardware and embedded systems, but I'd say I'm more software-inclined. I do know a few bits and bops about the digital design though.

At the moment I'm having problems with envelope.vhdl.
Essentially there was no power-on reset, and so during simulation clk_div started with the value of 0, and then it went out of range (clk_div - 1) and then of course the simulation crashed.
Now I set it initially to the value of PRESCALER (127). Could you tell me what is the initial value it should be reset to?
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elektromeister



Joined: Feb 18, 2013
Posts: 18
Location: Freiburg

PostPosted: Fri Mar 29, 2013 8:39 am    Post subject: Reply with quote  Mark this post and the followings unread

This sounds interesting. Are there any improvements for this synth?

Where do you see the advantage of FPGA synthesizers? I have recently found a report on an english website predicting FPGAs to be the coming platoform for electronical musics.
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