Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

I'm quite behind in this thread, sorry.... But is someone finally considering a port of Audacity? :)

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

I was writing about it in the hostmode thread (my second post I think), recording worked in ED with Audacity, attempts to playback crashed the device. But performance is rather sluggish, maybe this can be improved by recording to sdcard to avoid I/O conflicts with swap, or other settings in Audacity.

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

Hehe... told you so... :-)

Yet another great Maemo package I was unaware of... thanks for the tip, I'm trying it out !

Interesting find... although of course it just means that if we could use the DSP *and* bypass PA, then we would use even *less* CPU cycles that the stock media player :-)
Also, CPU decoding is very dependent on the codec type and its settings : flac, mp3 and ogg will have different CPU usage patterns for example. And also flac 0 vs. flac 8, or mp3 128k vs. mp3 320 vs.mp3 VBR0, etc
I wonder (but this is just a wild guess) if DSP decoding would prove less variable.

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

You are very right, the sad truth of the story is that there is nothing new at all here.

Ten years ago, the iRiver H1x0 had an optical spdif out (which could even be hacked into coax), and audiophiles were using them with their DACs.

Right as we speak, some Gen9 Archos tablets have an USB Host port and a modified Linux kernel that lets them play music to an external DAC. They are otherwise uninteresting as tablets go, and not very portable, but Archos made them more capable (probably quite easily) than all other Android devices.

So this is very well known and basic technology, and not even costly to implement. It's just that there is no market interest because the user base is so small (although if Apple were to "invent" the iDAC I'm sure even deaf people would buy it :-).

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

Status report on my call(s) for help... :-)

No sign of life on the Rockbox thread. Seems abandoned for good :-(

However, some people seem to follow Planet Maemo still.
Over the weekend I wrote a blog post about this project which was syndicated there.

Today I got some comments, one of which :

- was not spam :-)

- had some very interesting info and suggestions by a developer from Igalia who seems to know
quite a bit about the Maemo sound system...

Read it here and see what you think of his advice:
http://fredp.lautre.net/blog/2012/03...-music-player/

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

Interesting. so, 2 ways of doing what we want to achieve:

1. Make pulseaudio output to our external card (should be trivial, yet no one know how to do it up to date...)

2. Use mafw-gstreamer code (which is open, as it seems) and do little tweak, to change it's output. Should be quite easy for coders. 2a. Prepare way to change them on fly - "proxy" that igala suggested (NFC what he mean exactly), or script to switch between versions with ease.

Personally, I would prefer to use clean option 1, if someone would be able to actually achieve it ;) Yet, I must agree, that option 2 would use less CPU, due to omitting pulseaudio (although, I think difference would be neglible). More messy, as it included switching plugins on the fly (I wonder if it would be possible without reboots?), or some kind of proxification.

/Estel

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

By the way, what are you trying to achieve? :)
If the goal is lower power consumption, then CPU load indicator is not the best thing to look at. Because ARM core is not the only consumer, not to mention linux cpu load statistic won't give a complete picture of ARM core usage.

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

Another half-useful result of my experiments:

Looking at the code of the recaller widget, one sees that it is possible to use the output of a pulse sink (at least the internals) as a gstreamer source and therefore play it back via usb:

This plays back the output of the internal music player (perhaps any sound application that uses pulseAudio) through usb. There are two pitfalls:

• The normal output is not muted (minor problem I would guess and maybe solvable with alsamixer - as it should work on a lower level than pulse audio
• The audio stutters a lot (at least for me) - making this unusable for anything serious

Could someone try the above command on his/her setup? My device is not overclocked, and maybe it depends also on the external hardware. Be warned though, I got occasional reboots.

//EDIT:

To try this, just type the above in an xterm and play something back through the stock media player.

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

My modest goal would be to achieve decent battery life if we ever get this to work, given that h-e-n will already be gobbling down a good deal of juice :-)

I believe you, but I can't help thinking that if people put DSPs in mobile device, and stock media player uses it, there must be a reason, and something to gain :-)

Re: WIP: USB audio output - N900 as an "audiophile" portable music player
 

I will try it of course, but what a really strange command line !

Are those separators really exclamation marks ? :-)

I also have my doubts about the "audioconvert ! audioresample" parts on there, are they really necessary ?
I don't like the idea of the signal being reprocessed (what for ?), and it could possibly be the cause for the stuttering...