Sunday, July 3, 2011

Audio over HDMI

Since I had my Sonos network going (with occasional problems like Friday's power glitch) for several years before getting an OWLink HDMI network going, I haven't much used the HDMI's audio feature.

But this has always been a pain for several reasons.  One is that I have many possible audio sources in Kitchen, and Yamaha receiver doesn't output an analog tape out if the input is digital (such as from Dish box).  I have a small 3-way audio selector to select from receiver, Dish, or DVD player to go into the Kitchen Sonos box.  But if I am in bedroom, it's a pain to have to get out of bed and go to kitchen to change Sonos input source selection.  And worse if, as sometimes happens, a bad cable or such means I have to keep going back and forth to get problem debugged.  I think I had a bad cable problem this afternoon; after re-inserting the Dish cable into the selector box a formerly dead channel came back alive.  Or perhaps the problem is in the box itself...

In previous post I suggested boxes which can extract the audio from an HDMI signal.  But such a box isn't entirely needed, most TV's have audio output that can be connected to stereo.  (Yes, I can think of some advantages in having a separate box, but on with the story.)

So with Jazz Traditions from Dish playing, I finally had motivation to try the TV-to-stereo connection in bedroom.  That would also make showing movies and Dish in bedroom much easier.

But to be sure I wasn't introducing a ground loop, I needed to find an audio isolation transformer.  That meant digging in incredible snarled audio cable box, which took about 90 minutes.  As I pulled cables out, I re-wrapped them and used ties or size 33 rubber bands I recently purchased at Office Depot.  Until recently, I didn't have a good stash of rubber bands.  I always bought those "assorted" bags of rubber bands, which are worse than useless.  They always seem to be filled with the most useless sizes, with just a few of the right sizes.  As the right sizes get used up, you spend more and more time digging to find a useable rubber band or useable tie.  Now you see why my cable box was so disorganized.  Size 16 rubber bands look good also for heavier cables, and I got a bag of those too.

Finally I found a Radio Shack isolation transformer, which I put into service with a 6 foot Radio Shack audio cable, connecting the (Samsung 550 series) TV to my Tact analog input, removing the now unused FM tuner connection on Input 1.

I plugged in w/o attenuator first, and it was much louder than Sonos connection, so that worried me.  It doesn't say in Samsung manual what the audio output jack level is, I figured it might be 2V, and the Tact analog input only permits 1.6V (intended for old fashioned 1V sources) before clipping.  But all I could find were 3dB Harrison Labs attenuators, apparently all my 6dB attenuators are already in use.  Well 3dB would probably be enough, but to be sure I got out Fluke 86D peak holding multimeter and tried measuring.  On Jazz Traditions, the output wasn't getting much higher than 0.37V for awhile, so I tried some other Dish channels.  The loudest one seemed to be a Spanish speaking one, which hit 0.8V.

OK, so probably the output from the Samsung is 1V max, that's safe with older equipment.  But I thought it sounded better and more level matched with 3dB attenuators, so I kept them in.  From the TV, the signal goes through one 6' Radio Shack cable, an attenuator, a barrel connector, and then the cable for the Radio Shack isolation transformer.  The reduced level probably helps with the cheap isolation transformer.  It would be better with a Jensen isomax, but my only unused isomax is waiting to be used at work where my Mac Pro has already burned out an Radio Shack isolation transformer, but I figure the Jensen will be more robust.

Purist audiophiles would cringe at all of this, but I think it's adequate for satellite box or similar sources.  I thought it sounded quite good, at least as good as through Sonos which has to re-digitize analog inputs.

So I should get more 3dB and 6dB attenuators, and another Isomax.

Now I need to connect DVD player using HDMI instead of DVI, and connect living room TV to the stereo in living room in a similar way.  Then I won't have to fiddle with Sonos when watching satellite TV and DVD's.

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