dinsdag 15 mei 2012

Weak TOSLINK (S/PDIF) output on recent MacBook Pros

I have been using a surround receiver with a 10m optical TOSLINK cable and a 2006 model MacBook Pro without any problems for years. With my early 2011 17" MacBook Pro however, as well as someone else's 13" MacBook Pro from the same era, the receiver started producing frequent bleeping sounds, subtle audio drop-outs, and sometimes even downright refusing to work until it was ‘rebooted’.

I suspected all kinds of causes, including the cable or degrading components in the receiver. However, with a totally different receiver and cable of similar length, occasional drop-outs were also noticeable although this receiver was more robust and able to resume fast enough that it wasn't too jarring. After some more tests it became obvious that the light output from the new MacBook Pro is simply weaker than on older models and many other recent devices with S/PDIF outputs. This is especially visible when simply looking at the end of the cable when first plugging it into the new MacBook Pro and then one of those other devices. The photo shows the output of the MacBook Pro (top) and of a TOSLink repeater (bottom) through identical cables.

The 10m cable causes a considerable attenuation of the signal no matter what (Wikipedia mentions 10m as the limit for cable length). But with the old MacBook Pro, apparently the end result was still strong enough. The data sheet for the detectors in the receiver states that they expect at least -24dBm. My guess is that with the new MacBook Pro + the long cable, the output drops slightly below this, which is why it is just on the edge between working and not working. Some solutions are: a TOSLINK repeater to drive the long cable, a more sensitive detector with coax connection to the receiver, or a USB sound card with a stronger optical output. I settled for a repeater for which I made a USB power cable for extra convenience.
Another example where newer is not always better…

vrijdag 4 mei 2012

OS X Lion: fixing stuck wallpaper

One of the many small annoying bugs in OS X 10.7 ‘Lion’ that seem of too low priority to get fixed by Apple is that sometimes the desktop wallpaper gets stuck at the same image. When changing it in System Preferences, everything indicates that it has changed but still the same image stays on the desktop. A reboot fixes this and for some people (I suppose especially those used to working with Windows) this seems a satisfactory solution, but the more seasoned Mac users frown upon rebooting for something as trivial as this.

There is a more elegant solution, being only restarting the process that is responsible for the desktop wallpaper. This process is the Dock, and it can be restarted by either typing “killall Dock” in a terminal, or by using Activity Monitor. Mind that this could have some side effects. Eventually you will probably end up rebooting anyway to get everything right, but this fix will work if for some reason you badly need to change the wallpaper.

OS X Lion: oplossing voor vastgelopen bureaubladafbeelding

Een van de vervelende kleine bugs in OS X 10.7 ‘Lion’ dat blijkbaar van te lage prioriteit is om door Apple opgelost te worden, is dat de bureaubladafbeelding soms blijft steken. Als deze veranderd wordt in de systeemvoorkeuren wijst alles erop dat er een andere afbeelding moet verschijnen, maar de oude blijft staan op het bureaublad. Het ganse systeem herstarten is een ‘oplossing’ maar voor wie dit niet gewend is vanuit Windows lijkt het overkill voor zo'n triviaal probleem.

Er is een elegantere oplossing, namelijk enkel het proces herstarten dat verantwoordelijk is voor de bureaubladafbeelding. Dit process is Dock, en het kan herstart worden door ofwel “killall Dock” te typen in een terminal, ofwel door Activiteitenweergave (Activity Monitor) te gebruiken. Het is mogelijk dat dit wat neveneffecten geeft, maar deze oplossing is bruikbaar als u om een of andere reden dringend de afbeelding wil veranderen.