Why do most digital audio out / toslink ports FAIL to work with a "digital to analog audio converter"?


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Jun 24, 2021
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Marin County, CA
My hearing-disabled older client has a set of special earphones that require a 3.5" ("aux") audio out jack. It used to be plugged into her old TV. Her new cheap Samsung TV does NOT have an audio out AUX port for a 3.5" jack. (The new TV is connected to Xfinity box via HDMI cable.)

When I saw that both the Samsung TV and the Xfinity set top box had a Digital Audio Out (Toslink out), I went online and bought a "digital to analog audio converter". But when it arrived, it didn't work using the Toslink out on either the TV or the Xfinity box. (I made sure the TV was using PCM but no difference, and this generation of XFinity box did not have an "Audio Mode" section.)

So I brought the converter home for testing, and it failed to provide sound from the Toslink out ports on THREE Xfinity boxes and TWO televisions. But on the THIRD television (a newer Vizio)... it worked! I could hear audio thru the converter.

FYI, I have since realized that maybe I can use the analog out red & white RCA connectors on the xfinity box with a simple adapter cable (white & red RCA to stereo AUX) -- Plus I have also bought an "HDMI Audio Extractor HDMI to HDMI w/3.5mm AUX Stereo Converter Splitter" to increase my chances that I get it working, BUT:

What's the SECRET to getting a "digital to analog audio converter" working with a toslink out port? Why would the ports on 5 out of 6 devices fail? (NOTE -- on all the devices that allowed a choice for Dolby or PCM for the digital audio port, I chose it.)
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Dodgy box. Deaf to the optical signal?
Dodgy toslink cable making poor interface connection.

In one combination it worked, so something differed but nevertheless, one dodgy converter / cable does not make a rule that they are all poor?
Did you remove the plastic caps from both ends of the optical cables? If not could be they could still be in one or more the optical ports but by the time you got to the third TV they had come off?
On some TVs/devices you may also need to adjust a setting for the audio output destination as well as the format option for the optical. There is often a presumption that if you are trying to use the optical out you are feeding an external set of speakers, e.g. via an av receiver and so would not also want audio via the TV speakers. So some will have a 'destination' option or selector the active audio output such as 'speakers' 'optical' etc. which you may also need to set. Not all devices will output audio to the speakers and optical at the same time by default. Best guess you get audio on the one set as its default is to do both.
Thanks you guys -- Fred Smith, I made sure I had removed the caps before using. AndyCob, On 2 of the 3 TV's, I used the menu to switch from "TV Speakers" to "Digital Audio Out", but those were the 2 TV's that didn't work. (The 3rd TV, a Vizio, didn't have an audio mode switching menu.) And unfortunately, all four Xfinity boxes I have access too are older, so they don't have that X1 menu for switching between "HDMI Audio Output" and "Digital Audio Output: Optical/SPDIF". (Maybe the Toslink port was never activated by manuf?)
UPDATE - Got a new "digital to analog audio converter" box, and it WORKS with optical out on all three TVs at my house (with either RCA or optical cable) (as long as PCM output is selected, rather than "RAW" or "Bitstream"),

I also found the hidden non-xfinity menu to change audio mode from auto to "L-PCM" on the three Xfinity RNG200N boxes.

But the digital out audio still doesn't work -- the fast clicking sound (of what I"m guessing is RAW mode) persists.

So, while I'm probably going to have a workaround solution to my problem -- Anybody know why L-PCM mode on older RNG200N xfinity boxes don't work?
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