audiophile diy DAP?

[mcmurray]

Interesting ideas people.

I have been considering designing, from scratch, a 24bit desktop FLAC player (16bit files aswell) with built in DAC, ~1Tb of HDD.

Would a dual processor design say ARM like the iPod be useful to decouple the control logic from the playback engine? I envision a second processor would take care of buffering, decoding, signal processing and output to the DAC.

An expert in the area told me that quite a sophisticated ring buffering scheme will need to be written both for the input to the decoder and the output to DAC. It was also suggested that DMA be used to get the data from the HDD to memory and again for outputting from memory to the DAC. Sounds like a challenge

Just thinking out loud at this stage but first I think I will install linux and tinker with it as I'm pretty sure that will be the OS I will use. I have heard good things about RTLinux, has anyone here used it?

[ezkcdude]

I'm not sure you can make a portable audiophile-quality player. Forgetting about the control logic, processor, FPGA, SOC, let's just take a look at the DAC section, since most people around here are more familiar with that. Think about the board size of the DAC's considered "audiophile" quality. I won't even mention any (although I did once start a thread that still hasn't become sticky), but most of them are not that small. Good voltage regulation, low-jitter clocks, low-distortion output stages do not generally come in very small packages. Just think about all that needs to go into it. I have no doubt one could DIY a portable player, but in order to make it the size of an iPod, you really have to gut the audio parts to fit all the processing and have the whole thing fit in the palm of your hand. And forget about using boutique through-hole parts - it will be strictly smt affair. Just my two cents.

[mcmurray]

I understand, I have no intentions of making this thing small. I don't care if it turns out the size of a 5.1 receiver.

[threepointone]

yep, not gonna be small. might try to miniaturize it in the future, but unless we sacrifice some audio quality it probably won't get anywhere as small as most DAPs out there today.

I think some other people have been working on the DAP too--any news on those? Sorry to disappoint, but I haven't really gotten to work on the DAP since my last update. Until maybe november or so i'm far, far, far too busy to touch the project. To be honest, I really shouldn't be on head-fi right now =P After that, I should have loads of free time.

I admit, it's starting to smell a bit like vaporware =O

[mcmurray]

I think I will make my design single processor, not dual as mentioned before. I'm thinking maybe a Coldfire processor. Does anyone know where I could find a reasonably priced Coldfire Dev board?

[threepointone]

Dunno where the dual processor idea came from, but my current design (which has a lot to go) happens to be also based on the coldfire design. There might be some useful info in the previous posts in this thread (most importantly there's a link to a cheap coldfire BDM debugging cable somewhere in there). I don't know of any cheap coldfire dev boards, at least for freescale's audio processors that I've seen.

[antonyfirst]

What about the diy dap? I'd be really interested to get one.

[threepointone]

unfortunately, it's going to be quite a while before you can get one of the diy daps.

good news: i managed to get myself a mcf5251 eval board =) Should make things easier. I'm rather tempted to use the mcf5251/mcf5253 uCs for the final project, but I have no idea how DIYers would be able to solder these things. I'm not even sure if I could do it reliably myself if I set up a hot air gun/toaster reflow soldering system, especially for a chip with so many balls--anyone done bga soldering before?

[Cauhtemoc]

Originally Posted by threepointone

anyone done bga soldering before?

It can be done with a normal kitchen oven, a hot-air rework station, and a lot of patience. I have done it in the past, and I definitely wouldn't recommend it for a DIY project.

[error401]

Why not choose something like the AT91SAM9260 from Atmel? ARM9 core at 180MHz, and it's got basically everything the Freescale part has. Except it's easier to get; DigiKey carries it. The two big missing peripherals are the SPDIF interface and ATA controller, though if you're happy with Ethernet or SD, this part should be fine. I2S can be done with the SSC, and is explicitly mentioned in the documentation, and I know that was a big appeal for choosing the Freescale part.

This chip is significantly faster than the Motorola as well, and I think it's probably fast enough to run embedded Linux with proper networking and standard user-mode FLAC etc. decoding libraries and some plain-jane C code to tie it together. You might end up having to write some simple drivers, but these shouldn't be too difficult.

iPod uses an ARM core, so if you wanted to, porting Rockbox to your device would likely be no more difficult than targetting Coldfire. In fact, there's probably more ASM optimization in the ARM port. I bet the GNU toolchain for ARM is probably better than the Coldfire one. ARM seems to be a lot bigger than Coldfire in all sectors but mobile gadgets, where they seem to have about equal share.

Check this guy's work out: http://www.mikrocontroller.net/artic...MP3/AAC_Player

[labmat]

The nice thing about the Atmel is the programing hardware is readily available and inexpensive. Nice for DIY!

[casainho]

Hello :-)

I would like to invite everyone to look at our Free/Open hardware dap for use with Rockbox:
Rockbox Player

If you can help, please join team and let's build the best Free/Open hardware dap which will work with the best open source firmware for mp3 players, written from scratch, the Rockbox ;-) :-)

Thank you.
---
Casainho - http://www.Casainho.net

[Basil101]

My idea for a DAP; why not use a Via pico motherboard as the base, it can run any x86 OS (a custom linux perhaps), it has USB ports for a DAC to connect and there are USB screens readily available.
The motherboard is a typical Via in that it is very power efficient therefore battery power is possible (these are used in carputers that run from a 12V lead acid).
Input could be from something like this mini wireless keyboard or just buttons on the casing.
Personally I would have a motherboard, 60GB 2.5" HDD, running from a wallwart/PPA battery board, a USB powered Alien DAC which outputs to a standard 3.5mm jack and a mini wireless keyboard. Case the whole lot in a an enclosure like the hammond 1455N1601 for a great sounding luggable DAP. To get music on a USB CD drive would suffice.

Or buy the kit and mod till your hearts content.

[00940]

Anyone considered the VS1033 ? It has problems (it resamples everything to 48Khz and only accepts flash cards) but also has an I2S output so you can add your favorite dac directly to it.

[ericj]

Resampling, especially in short jumps such as 44.1khz to 48khz, is BAD. Causes aliasing unless done with extreme care.

Basically, in order to avoid alisaing when making a sampling change of +3.9khz, you have to upsample to a much higher rate (like 112khz, iirc), and then downsample back to your target sample rate. Google "helmholtz" "nyquist" "sampling theory" and "aliasing" for details. The math here is quite solid.

Best case scenario it only damages fidelity a little. Worst case scenario it sounds terrible. You cannot improve the quality of the stream by manipulating it. You might reduce some of the distortion at the DAC, but you've damaged the stream to do it.