After extensively breadboarding a PT2399 circuit and never being 100% happy, I decided I should probably give a DSP based delay a go.
I'm happy programming in C for micro controllers and Verilog for FPGA's, but I didn't think these help too much with simple audio DSP chips. The Spin FV-1 seems to be discussed a lot. I've had a fair trawl through the web and this forum and it seems this could be a good option. Here are my questions (which I have tried searching for the answers for already):
- Before going down the FV-1 line, are there any other DSPs to consider with ADC/DAC built in that can be programmed in C rather than ASM?
- The FV-1 thread on this forum has a nice looking single sided PCB, this looks like a good starting point. What is the mechanism for downloading firmware to the 24LC32A Eeprom? Do I need programming hardware? What software?
- I would like to experiment with reverb and delay primarily. What length of delays should I be able to achieve with the chip?
- The eTap2hw looks great. However I can't quite figure out if this firmware can be downloaded free or has to be paid for?
Quote from: scintillation on December 28, 2014, 02:14:47 PM
- The FV-1 thread on this forum has a nice looking single sided PCB, this looks like a good starting point. What is the mechanism for downloading firmware to the 24LC32A Eeprom? Do I need programming hardware? What software?
I believe the PicKit2 programer has been used quite successfully in programing the EEPROM for the FV-1. A good person to ask would be slacker. He has pretty good knowledge on this. ;)
@scintillation, I noticed that you found your way over to my forum to get SpinCAD Designer. I think you will have a blast creating delays with this tool. I have made some really wild things with filtering in the feedback path, etc.
The FV-1 has 32768 memory locations, so at 32768 Hz sampling frequency, you get 1 second of delay.
There is a way through sample rate reduction to get up to 8 seconds of lo-fi delay. I haven't made that into a SpinCAD block yet. You could find it over at the Spin forum or knowledge base.
-The FV-1 running at the standard clock freq can have a delay of up to one second.
-The Eeprom can be programmed using a Pickit2 or if your pc has a serial port you can make your own programmer for a few pennies and use a free program called ponyprog or it could be ICProgram.
-The single sided PCB you mention has the Eeprom programming connections on the PCB so that the Eepromcan be programmed without removing the PCB or chip.
-The hex file for the eTap2HW can be distributed but the ASM files are not allowed.
Quote from: scintillation on December 28, 2014, 02:14:47 PM
- Before going down the FV-1 line, are there any other DSPs to consider with ADC/DAC built in that can be programmed in C rather than ASM?
No high grade adc/dac (altough its not impossible to get some good audio codec) but you can check:
This:
http://www.pjrc.com/teensy/td_libs_Audio.html
-333mS max, dont know if you can connect block in series.
Programmed in C and Arduino
And this:
http://www.diystompboxes.com/smfforum/index.php?topic=109314.0
Programmed in C and (if any) ASM
Quote from: scintillation on December 28, 2014, 02:14:47 PM
What is the mechanism for downloading firmware to the 24LC32A Eeprom? Do I need programming hardware? What software?
For a cheap way to program the EEPROM have a look at this thread http://www.diystompboxes.com/smfforum/index.php?topic=108891.0 (http://www.diystompboxes.com/smfforum/index.php?topic=108891.0) one of those circuits and a cheap USB to serial cable is all you need, both will also work with a real serial port if your computer has one.
In principal, integrating an ADC/DAC into the DSP chip is a "bad" idea, since you can't decouple it properly, or ensure separate ground planes, etc. This is why the majority of DSP designs allow the designer to pick their own ADC/DAC/codec. It's not a "good" investment to design and manufacter a DSP chip that has it's own codec.
That said, spin semi saw a niche market where enough people wanted an all-in-one chip, and decided to take the risk with the FV-1 (custom chip design/fabbing is stupidly expensive!). It paid off I think! But because of how niche it is, and some of the disadvantages, I don't think we're gonna be seing more of these anytime soon. I may be wrong.
the FV-1 with spincad designer is probably your best bet for starters. If you really want to experiment with C, then you'll have to deal with external codecs/ADC/DAC.