Audio Theory, Setup, and Chat > Optical to Analog Digital Converter/Adapter Problem
ridgeland's Avatar ridgeland 05:27 PM 09-07-2012
A friend who occasionally asks for my advice on problems he is having with either his computer or home entertainment system has again asked for my advice. He had in the recent past purchased a new Panasonic plasma HDTV and has just now tried to connect his old wireless headphones to the new TV. In doing so, he discoverd that the new TV does not have the stereo analog audio output which is required as the input to the old headphones. After talking to me about it and finding out that the TV has only a digital optical audio output, I recommended that he purchase an optical to analog converter to be placed between the TV optical output and the analog input of the headphone base. The converter that he purchased is a Sanoxy Digital Optical/Coax to Analog RCA Audio Converter Adapter but when he uses it with over the air broadcasts via theTV's tuner, he only gets "white noise" with crackling and popping out of his headset. The TV display video in this setup is OK. When using a DVD player as the TV composite audio/video input source rather than the OTA broadcast, the audio comes through to the headset OK and the TV display video is fine. The problem also exist when the analog output from the optical to analog converter is connected to a stereo amp rather than to the headset base. These same problem occurs when using the optical audio output from a second TV of a different manufacturer. Any advice or fixes for this problem will be greatly appreciated.

MarkHotchkiss's Avatar MarkHotchkiss 08:33 PM 09-07-2012
Hi Ridgeland,

Some TV stations broadcast in stereo, but others broadcast in Dolby-Digital 5.1. Some TVs (like mine) will only output the encoded DD-5.1 through the optical output, while others will let you decode DD-5.1 to stereo for the optical output. When he tunes in a TV station, his TV should be able to show him what type of audio is being received. If DD-5.1 is indeed his issue, then here are his options:

1) Weed through the TV's setup menus, looking for the option to always decode down to stereo for the optical output.
2) Get a optical-to-analog converter that also can decode DD-5.1, like THIS.
has7738's Avatar has7738 08:34 PM 09-07-2012
What's probably going on is the TV is just outputting the digital audio stream as it exists without decoding it into PCM, which is what the converter needs. So any digital audio signal that is encoded in Dolby Digital, for example, comes out of the optical port as just that, which the converter would see as noise. That optical port really isn't for use that way, it's a way to get the raw digital signal back to an AVR which has the ability to decode all forms of digital audio. There's an outside chance that there may be a setting buried in the TV's setup menu that controls exactly what comes dripping out of the optical port, and there may be a way to set it to PCM, but I kinda doubt it. Just about any current AVR with an optical input would handle the signals just fine, and many of them have headphone jacks.
commsysman's Avatar commsysman 06:58 AM 09-08-2012
One thing you need to be aware of, and there seems to be some confusion about here is that the optical audio is 2-channel 16-bit PCM ONLY! No other formats or enhancements are supported.

Optical audio is NOT multi-channel !!!
arnyk's Avatar arnyk 11:00 AM 09-08-2012
Quote:
Originally Posted by commsysman View Post

One thing you need to be aware of, and there seems to be some confusion about here is that the optical audio is 2-channel 16-bit PCM ONLY! No other formats or enhancements are supported.
Optical audio is NOT multi-channel !!!

The above is completely and totally false. Optical supports a wide variety of stereo and multichannel digital audio formats, including many surround formats such as Dolby Digital and DTS. It is not as flexible as HDMI, but it does much more than just 2-channel 16-bit PCM. For openers, it does 24 bit PCM.
MarkHotchkiss's Avatar MarkHotchkiss 11:01 AM 09-08-2012
Quote:
Originally Posted by commsysman View Post

One thing you need to be aware of, and there seems to be some confusion about here is that the optical audio is 2-channel 16-bit PCM ONLY! No other formats or enhancements are supported.

Optical audio is NOT multi-channel !!!
Actually, the optical cable, although originally designed for 2 channel PCM, can also carry core-DTS and Dolby-Digital 5.1, in their compressed format. In the early days of DVDs, before HDMI, optical and coax were how we got surround out of the DVD players.

Edit:
And Arny's post brought up another thing: S/PDIF, from the start, supported 20-bit PCM, with the capability for 24-bits using four 'option' bits.

Funny: Four hours with no reply, and then Arny and I post within 9 seconds of each other.
ridgeland's Avatar ridgeland 09:00 AM 09-19-2012
Thanks to all of the great information and advice from online-shashki forum members, a successful solution to this problem has been found. Since my friend that had the problem as described in my original posting lives in Texas and I live in Tennessee, it took some time time in communicating and discussing what we had learned on the forum in order to come up with a "workable" solution. In the end, it occurred to me that, rather than purchase a device specifically designed to decode only the audio content of the digital broadcast signal, a less expensive solution was available. From earlier "testing", we had found that the analog stereo audio output from his DVD player, when connected to the TV's analog stereo input and then out via the TV's digital optical ouput to a "optical to analog stereo audio converter" and then out to the headphone base, would pass the audio through. Given this, it seemed reasonable that, rather than purchase an special digital audio decoder, a digital to analog signal converter such as had been purchased and used by many of us during the transition from analog to digital TV broadcast, should also work. Since I no longer needed any of the converters which I had purchased during that transition, I sent him one of my "leftovers". He put a "splitter" in his antenna "feed", running one output of the "splitter" to his TV and the other to the digital to analog converter. The composite video and analog stereo audio outputs of the converter were then connected to the corresponding inputs of the TV where the DVD player had previously been connected. The DVD player was then connected to the TV's component video/analog stereo audio input. With this "lash up", he simply uses the "remotes" for his TV and/or converter to configure the TV's input and the converter channel selection. He says that, surprisingly, the TV video quality difference between that coming from the converter and that of the direct digital HD broadcast is barely noticeable, if at all. Most of all, his original problem with using his old wireless headphones has been solved.
Up
View Full Version