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Old 14th December 2013, 02:41 PM   #1
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Default DIY Audio Recorder

Which micro-controller should I use if I want to record four channels of 24-bit 96kHz audio to a micro SDHC card? Thank you.
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Old 16th December 2013, 04:56 AM   #2
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Join Date: Feb 2008
Location: Jackson,michigan
There are quite a few out there that could do that.

I am new at it, but I am planning on building a digital multi-track system as my main goal as well.

If you just want to record and playback this won't take a lot of MCU power.

I found a really cool 16bit quad delay project using three MCU's from Microchip here,

Seb's Synth-DIY Pages - 4xD

One is used for house keeping and one for each two channels of audio.

There is also some sample audio files on the page of the device and it sounds very impressive!!!

The web page shows everything and it is all open source and has all of the needed software files and schematics with board layouts.
I just found it about two weeks ago!!

I just last week got a ST32F4-Discovery Kit, it has a 32F429 ARM Cortex4 180Mhz MCU from ST on it, as well as a 800x600 TFT display that is also touch controlled.
And It only cost about $33!!!

STM32F429ZI High-performance and DSP with FPU, ARM Cortex-M4 MCU with 2 Mbytes Flash, 180 MHz CPU, Art Accelerator, SDRAM, TFT - STMicroelectronics

Here is the link to the board,

32F429IDISCOVERY Discovery kit for STM32 F429/439 lines - with STM32F429ZI MCU - STMicroelectronics

Once you start getting into the 32bit MCU's you need to know C and that is where I am at right now, trying to learn C.

I think that such a system could be made using one of Microchips super fast 16bit MCU's as well.
I have a quite few of those too, but, as I said I am just stating at this.

I think my first attempt will be a 8 channel 12bit system with just a few parts in order to get the hang of everything.

Then do a 16 bit version and then graduate on to the 32bit MCU's and 24bit data.

I chose parts that have the most ram and flash I could as well as the highest speeds in the 8 and 16 bit versions.

The 16bit versions I have does 70mips and also has a DSP built into in it as a well.

The 24EP256GP202 is a 3.3v part and does 70mips in a 28 pin SOIC package.

The 24HJ128GP502 is a 3.3v part and does 40mips in a 28 pin PDIP package.

They have packages with more I/O pins as I just got what is easiest for me to work with right now.

This should be able to do it as it is just transferring data back and forth.
I had even seen this very same family of chips used in a high resolution RTA device (FFT).

Cheers!!!

jer
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Old 16th December 2013, 07:43 AM   #3
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Thought about it for a while, bought a ready-made unit from Tascam.

We use the STM32 processors at work. They are pretty good. In particular you get a ready-made "FATFS" library that implements the FAT file system allowing you to read and write SD cards. I don't know if the 16-bit Microchip parts have this.
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Old 16th December 2013, 11:40 AM   #4
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The only reason I want to do this is because of the poor sample rates that the commercial devices have.

Good point about the files system this is already built into the 32F4-discovery board with a separate USB port just for a flash card.

I was thinking that you would not even need a file system if it worked like a tape deck and when you were done recording and playingback you could use a routine to dump it as a wave file via USB for further processing in a DAW.

In my system I was thinking about a stackable system so that more channels could be added at any time and use a large stick of ram per unit and have everything SMPTE time code locked to my analog 16 track taped deck.

There are many possibility's!!
it all depneds on how much time you want to record and wether or not you want to do more processing on the signal realtime or not.

Great Project keep us posted!!!

jer
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Old 17th December 2013, 04:13 AM   #5
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Join Date: Dec 2013
Thanks for these pieces of advice! They are really useful.
Actually I need a Zoom H4n (or something similar) as I want to run dual system for my DSLR. Those commercial products are too expensive so I decided to build my own recorder. It's cheaper (and provides more fun). I have finished the other parts of my design and only the 'recording' part is left.
Anyway, I have very briefly read about the MCUs. They are more powerful than I have thought. I didn't know that there are libraries available so I think I can handle more. Now I would go for SDXC and WAV file instead of SDHC and RAW files. I guess I might go for a more powerful MCU, just in case. Maybe one day I would have spare time and upgrade the programme to handle more functions. Those MCUs are still affordable for me.
I might just post here when I have finished the whole schematics and the programme. I am quite busy lately
Thank you very much!
P.S. Please forgive me if my English does not make sense. I'm not a native speaker :P
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Old 17th December 2013, 03:10 PM   #6
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Location: Jackson,michigan
Yes, I am very interested in seeing your progress !!!

I started with the idea of using some of my Older ISA bus PC's that run from 200Mhz to 400Mhz because are easy interface to compared to the PCI bus structure.

But after researching what is available in the modern MCU world I am just blown away!!
Not only with speed, But their size and complexity as well!!
Not to mention that they cost next to nothing for what they can do!!!
30 to 70 MIPS on a little 28 pin DIP and more.......Outstanding!!

I have been googling up "Projects for PIC" and it is amazing at what I have found and the one that really intrigued me was a Realtime RTA and the code was published with it as well.
I couldn't believe how short the code actually was.
I even found and downloaded a ZIP'ed project with some library's to do Audio Filtering and EQ's, I think that one was on the Microchip website.

I Had an ART SGE guitar processor back in the day (1988) and it only had a 20Mhz DSP from TI in it.
It did Realtime Voice Transposing....That was a First for me and the times....I just loved that thing!!!

I am basically an analog buff, But if I can do everything using 24bit and at (at least) 192Khz that would suit me just fine !!!!
The price of tape and replacement parts for my machine's are not getting any cheaper, Let alone trying to find them!!
I already have a good mixer (Mackie 32-8).

Good luck and I hope to see your results!!!

:Cheers:

jer

Last edited by geraldfryjr; 17th December 2013 at 03:23 PM.
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Old 22nd December 2013, 04:41 AM   #7
dangus is offline dangus  Canada
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Modifying a Zoom might be easier, if the only real problem is poor power supply filtering for the analog stages and ADC. Out of the box, the H4N doesn't even achieve 16 bit quality, let alone 24 bits. I was tempted to buy one and try to improve it, but I figured that if Zoom can't be bothered to get the fundamentals of audio capture right, what else have they cut corners on?
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