Some Stereo Tests


Yrx

the Happy Conqueror
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Well, I just got my GP2X a few days ago, and today I decided to try out some music on it. I had seen that there were some stereo problems while browsing on here and the wiki, and sure enough, the channels were reversed, they kept switching, and there was a small clicking kind of noise every few seconds. So the first thing I did was try and download the stereo fixer utility from the archives. If it helped at all, it was very minimal, but I wasn't really expecting much due to the release date. So then I downloaded CraigAmp, hoping that another program might solve the problem.

The first thing I did (for some reason or another) was underclock to 100 mhz. I still had the switching channels during play problem, and the channels were still reversed. When I tried changing the clock settings while it was playing, it froze, and I had to power down my GP2X. When I turned it back on, I went up to 150 mhz. The switching midplay problem stopped immediately. It didn't come back, even when I went as low as 115 mhz (although it turned out that it still did with a couple songs on this setting). Of course, the channels were still reversed, but my headphones are completely reversible, so that doesn't really bother me. :lol:

All the songs I tested this with were between 128-192 kbps, mp3 and ogg, and a mix of fixed and variable bit rate. 130 mhz played all of them perfectly.

I didn't really see anything like this with a quick search of the boards, so I figured I might as well share. I did see a post from about a month ago saying that the channel switching also happens on OldPlay, but I haven't tested that out. What it seems to me is that the channel switching can be fixed if the program is efficient enough. Of course, the channels are still reversed, but this is a start, right?

(By the way, I'm not particularly endorsing CraigAmp. I was too lazy to test anything else. ;))

Oh, also by the way, was there a program I saw that lets you change the default music application? I thought I saw something like that, but I can't seem to find it now...
 
Yrx said:
Well, I just got my GP2X a few days ago, and today I decided to try out some music on it. I had seen that there were some stereo problems while browsing on here and the wiki, and sure enough, the channels were reversed, they kept switching, and there was a small clicking kind of noise every few seconds. So the first thing I did was try and download the stereo fixer utility from the archives. If it helped at all, it was very minimal, but I wasn't really expecting much due to the release date. So then I downloaded CraigAmp, hoping that another program might solve the problem.

The first thing I did (for some reason or another) was underclock to 100 mhz. I still had the switching channels during play problem, and the channels were still reversed. When I tried changing the clock settings while it was playing, it froze, and I had to power down my GP2X. When I turned it back on, I went up to 150 mhz. The switching midplay problem stopped immediately. It didn't come back, even when I went as low as 115 mhz (although it turned out that it still did with a couple songs on this setting). Of course, the channels were still reversed, but my headphones are completely reversible, so that doesn't really bother me. :lol:
I work for Wolfson who make the codec i the gp2x and the clicking/channel swapping is almost certainly caused by a fifo in the ARM not getting filled in time to make the next slot on AC97. This will of course happen as you increase the CPU load, ie running at 100Mhz might have your cpuload at 100%, wherease running at 150Mhz you will only be at 66% and therefore leaving more time for the FIFO to be filled on time.

This is an inherant problem on pretty much all ARM AC97 and I2S implementations and the deeper the fifo's the better. I havent looked at exact details of the MMSP cpu but it might be you can improve the situation by making the fifos signal when they are almost empty earlier.

As for the left/right swap that is probably a wiring screwup. I cant get hold of the data sheet for wm9711 just now. But a lot of out codecs have a internal swap bit. To take care of wiring screwups.
 
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The left/right channel swapping is not due to a wiring problem as I have solved this by enabling the RAM timings hack and running at 100MHz. I use gmenu2x so this is a rather simple task.

I believe the channel switching happens only in music files that are encoded with VBR - Variable Bit Rate, and when more RAM is allocated for higher bitrates that change dynamically during the song, the popping/channel switching occurs. The RAM timings hack resolves this issue by enabling the RAM to be faster at no power cost, but it is a tad bit unstable compared to the default timings. But if you run the music player with it, there's no cause for concern. I've never had the RAM timing hack cause the music player to crash before, and doubt it ever will.
 
In my experience, whether the song was VBR or not had no noticable impact on the popping/swapping. It did it on all of them. :lol:
 
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