Rockbox as a USB audio device?

[thomaspf]

Hi,

I am wondering whether there has been a discussion about using your rockbox device as an external audio device to your PC. I am a happy owner of two H120 but recently I have been toying with the idea of getting a Headamp Pico for use with my laptop.

The crazy thing is that almost all components in that external USB dac/amplifier also exist in the most portable media players.

Today Rockbox only implements the code for a USB mass storage device but I am wondering whether it would not be possible to also implement the code to make a portable media player appear as a standard USB audio device. The sound quality you would get from almost any portable player would be a lot higher than from the built-in sound cards in many computers.

I can not code this but I am wondering what you think?

Cheers

   Thomas

[saratoga]

Hi,

I am wondering whether there has been a discussion about using your rockbox device as an external audio device to your PC. I am a happy owner of two H120 but recently I have been toying with the idea of getting a Headamp Pico for use with my laptop.

The crazy thing is that almost all components in that external USB dac/amplifier also exist in the most portable media players.

Sure, but they're little different then the parts already in your laptop.  DAP DACs and laptop DACs are very similar, both in design and performance.  If you need an amp for your laptop, you'd almost certainly need it for your DAP as well.

Today Rockbox only implements the code for a USB mass storage device but I am wondering whether it would not be possible to also implement the code to make a portable media player appear as a standard USB audio device.

Theres the beginnings of a USB audio driver for rockbox.  You'd have to finish working on it, but its certainly possible.

The sound quality you would get from almost any portable player would be a lot higher than from the built-in sound cards in many computers.

Better then a few built in cards, but not most.  DAPs have low hiss because they're battery powered, but thats about all they do well, and if you ran it off a USB cable, you'd likely lose even that advantage since you'd be running off the PC power supply.  They are, after all, built out of what is essentially a low end PC DAC.

[Llorean]

And, as a note, this isn't a feature the H100 series will ever see, since its UMS mode is hardware controlled, and not something subject to Rockbox's internal USB stack.

[thomaspf]

Bummer...

Edit:  Now that I thought of it a bit more. Would it be possible to write a USB audio host stack? In that case you could use the media player as a source for external USB audio devices. That would be pretty nice too.

Cheers

   Thomas

[AlexP]

All the H100 can be is a UMS device.  This is a hardware limitation.  If your external usb device can read a USB hard disk, then sure.

[gevaerts]

Edit:  Now that I thought of it a bit more. Would it be possible to write a USB audio host stack? In that case you could use the media player as a source for external USB audio devices. That would be pretty nice too.

All of this is somewhere on my list of things I want to do some time, but as people said higher up, it's always dependent on what hardware a particular player has

[nullstring]

Has any work been done on this?

Particular DAP's, such as the ipod 5G w/ a LOD and possibly a diymod would offer a high(ish) quality solution for an external USB DAC.


How hard do you think this would be to implement? I'd really like to see this.

I am gonna do some research on USB communication and audio drivers, but it seems to be a hard topic to google.
Feel free to share any insight of the correct direction to look in, etc.

[gevaerts]

The specification for usb audio is at http://www.usb.org/developers/devclass_docs

[Vchat20]

Regardless of sound quality, another possible pro would be to use the headphone amps in these players and possibly even use the players own volume control as an in-line volume control.

My laptop has a pretty lousy headphone amp that can only push comfortable volumes to the dinky little earbuds but my good over-the-ear cans are JUST audible at maxed out volume (often have to kick up the preamp in winamp's EQ to help as little as it can).

The Sansas (esp. the c200 line) would make a nice portable formfactor to act as a usb sound card and headphone amp. And then when it's not being used in that fashion it goes back to being an mp3 player.

If I had any programming expertise I'd jump on this myself. There is a patch up from some time back dealing in making a dummy usb audio stack which just showed up as an audio device to the host but didn't do anything else. Might be worth taking a look at?