Tonys Mac Journal

4jan07
I'm going to try to record my experience working with the Macs at FreeGeek. This will be mostly subjective train of thought, first impressions, immediate reactions, that sort of thing. This first entry will be a recap of the things I can remember from that past couple of weeks.

Audio Skipping
iMacs/PowerMacs with CPU speeds less that 450MHz seem to have problems playing CDs using SoundJuicer and RythmBox, the CD ripper and CD player installed with Ubuntu. Playback audio will 'skip', producing gaps of a few seconds, and may even cease altogether. Loren has been able to solve this by replacing CD drives in slot loading iMacs and PowerMac Towers. I have solved it by installing gxine and manipulating its configuration parameters, specifically the increasing the number of buffer blocks and increasing the value of media.audio_cd.drive_slowdown in the xine configuration. The xine configuration file usually shows up in the users home directory as .xine/xine_config. gxine provides acces to most of the configuration parameters through Preferences in its menu. There are several levels of parameter control in Preferences. The level named Master of the Universe allows a the most access. I have been increasing the slowdown parameter from 4 to 12, and incrreasing the number of buffer blocks from 230 to 500. Both of those were guesses on my part. Increasing the number of bufer blocks may not be necessary.

I don't know exactly why either of the solutions works. Some of the CD drives Loren has been using as replacements are much newer drives, and probably offer better performace features. The fact that there appears to be a configuration solution makes me think that the existing CD drives are not bad, but have lower performance that needs help in software. There are several different models of CD drive use in the iMacs

There are several problems with the gxine solution with the lower CPU speed Macs (233-400MHz). gxine has a visualization feature that competes with audio for CPU cycles. Turning the visualization off reduces or eliminates the 'skip' problem. Visualzation control is under the View drop down menu, but changes there do not persist across gxine restarts. I haven't found a way to make the visualization change permanent.

5jan07
iMac G4/700 Flat Panel It's that half-basketball-long-neck thing with the flat-panel display on the top of the neck. It came in on 29Dec06. 70MHz PPC, 40G hard drive, 256 MB, DVD/CD. Runs Mac OS X just fine, but refused to boot the Ubuntu 6.10 installation CD. Yesterday and today Loren swapped out the hard drive for a wiped drive from the store. He also (miraculously) found a 256MB SODIMM to upgrade it's memory, with the goal of creating a very nice high end PPC machine.

It turns out this is a very weird machine, even for an iMac. The system memory is a SDRAM DIMM (regular PC memory). The expansion memory is SODIMM (laptop style). The expansion memory and wireless network card (airport) are underneath the bottom cover plate, which is easily removed. The drives and system memory are underneath a second bottom plate below the first one, and is much harder to remove and requires application of thermal paste to a thermal transfer plate when re-attaching it. The graphics controller is an nVidia GeForce 2 400 MX, which the Ubuntu PPC install CD apparently doeesn't know how to deal with. The CD starts to boot normally, gets to the part that says loading ramdisk and then hangs indefinitely.

This version of the iMac was not in production very long. I'm thinking we won't see very many of them, and should probably not spend a lot of resource trying to solve this. It's more of a 'special project'. There may be a way to solve it, but it might involve detailed knowledge of the Ubuntu PPC boot process and maybe even some knowledge about how to manipulate OpenFirmware.

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