Does It Make Much Difference What Type of Audio Output Is Used for TV Streaming? - Analog vs. Coaxial vs. TOSLINK S/PDIF?

I’m probably one of the most ignorant people around when it comes to audio standards and streaming but PCM is the method by which the audio encoding is digitally transmitted, kinda like AAC vs. MP3.

I got some vague idea in looking at the capabilities of the Toslink S/PDIF powered audio splitter that I just bought on Amazon to divide the Toslink output from my TV for my speaker amplifier and the ReSound TV Streamer 2. The splitter that I got can only accommodate PCM sampling frequencies up to 96 kHz whereas with 4K TV’s, apparently the maximum possible output can be at least 192 kHz (and at least one Amazon reviewer says that the splitter that I got can unofficially handle that)-the reviews mention the possibility of selecting PCM output quality via the TV’s setup menu. There are other limitations as to the type of audio formats the splitter can handle but since I have an old large screen TV (2008 Sony), I doubt whether my $21 Toslink splitter will have to deal with the latest and greatest audio streaming formats unless I get a new TV!

A PCM stream has two basic properties that determine the stream’s fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are taken; and the bit depth, which determines the number of possible digital values that can be used to represent each sample.

Pulse-code modulation2

Pulse-code modulation (PCM) is a method used to digitally represent analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps. Alec Reeves, Claude Shannon, Barney Oliver and John R. Pierce are credited with its invention. Linear pulse-code modulat...

PCM is digital. It’s a generic, public domain coding scheme as opposed to Dolby Digital encoding which requires a licensed chip to decode. So most 3rd party digital input devices use simple PCM, and I think the TV Connector is one of those.

A simple powered TOSLINK splitter should be entirely agnostic to the type of encoding as long as its switching components can keep up with the bandwidth of the signal. Perhaps lower priced ones have bandwidth limitations and fail to conduct the higher sampling rates.

Coaxial digital (which to my knowledge the TV Connector does NOT support) is perfectly fine for home audio use. There would have to be a staggering amount of EMI in the environment to affect a 3’ run of cable. And remember, it would cause dropouts, not any qualitative degradation of the audio. Digital reproduction is either there 100% (subject to error correction abilities), or else it can’t output anything where the data and error correction fails.

IMO, good ol’ analog audio is just fine for home use, especially for hearing impaired people who already have limitations on the dynamic range. The noise floor is lost on most of us.

Especially for TV use. Not exactly Hi Fi.

@haggis said:

The TV Connector can only receive and transmit audio in mono or stereo. Please make sure that no Dolby digital or DTS audio settings are used by the TV (or audio device). If present, these audio signals will be indicated by a blinking red LED indicator light on the TV Connector. Please change the audio signal to stereo (PCM) in the audio settings menu of the TV.

Perhaps the ReSound streamer is just a tad bit more capable than the Phonak TV connector? Here’s what the manual says are the digital audio streaming capabilities of the ReSound TV Streamer 2 - it can accept the most basic 5:1 Dolby Digital but you only get to hear it in stereo (unless unbeknownst to me the ReSound HA receivers have some incredibly clever way of emulating 5:1 sound in your ear canals! <<<just kidding>>>

The TV Streamer 2 supports both analog and digital audio input. When using digital audio input the following formats are supported:

Stereo PCM

• Sample rate: Up to 192 kHz
• Sample resolution: Up to 32 bit

Dolby Digital

• Channels: Max 5.1
• Bitrate: 32 kbs to 640 kbs
• Sample rate: 32, 44.1, and 48 kHz

Note: Dolby Digital Plus (requiring an HDMI interface), Dolby TrueHD, Dolby Pro Logic, Dolby Digital EX, Dolby Digital Surround EX, and AAC (Advanced Audio Codec) are not supported.

Edit_Update: The powered TOSLINK splitter that I got on Amazon is even a bit more capable in its digital audio capability:

Support Dolby Digital & DTS 5.1, Dolby Digital Plus; Support PCM Stereo 32kHz, 44.1kHz, 48kHz and 96kHz; plug & play

But as to my TV/speaker audio problem, I haven’t even bothered to check recently what format my TV is outputting to my amplifier. Presumably in 2008 when I set the TV up, I picked an output format compatible with my amplifier but that may be the source of DVD/Blu-ray speech dialog not sounding so great through the amplifier’s speakers as compared to my TV streamer… (trying to stake my claim to extreme audio ignorance!). We shall see! Guess for stereo listening through my HA’s, I should go with PCM as it’s uncompressed whereas Dolby Digital 5.1 is compressed - but I would lose some of whatever spatial resolution is supposedly in my home speaker system if listening thru Dolby HA TV stereo streaming with some external mic input from the 5:1 Dolby speaker system thrown in… Is PCM better than Dolby Digital? - Blu-ray Forum4

The reason I said PCM is the Phonak TVLink only works when the TV sound is set up in PCM. I had read it was mono or stereo but not Dolby digital.
Anyway, you smart guys go on with the discussion.

Yes. The Resound streamer looks a lot more capable.

And the TOSLINK splitter lists all those protocols because AFAIK it doesn’t care what protocol is carried by the bits. Only the bitrate matters. But perhaps those proprietary protocols (Dolby etc. and DTS 5.1) imply their own bitrates.

I wouldn’t worry about Dolby compression. If your streamer can handle it, use the most sophisticated encoding that both your streamer and amplifier will handle. Those encoding protocols are made to enhance the listening experience. I don’t think you’ll perceptibly lose anything by streaming them to your HA’s. And you’ll retain the decoding for multichannel stereo to your speaker system.

@jim_lewis said:

Apparently, the Blu-ray player negotiates bitrate with the amplifier. So it will be interesting to see what happens when I insert a TOSLINK splitter in the path whether I get stereo in the path going to the ReSound TV Streamer 2 and “Surround Compatible” PCM still going to the Yamaha amplifier and same deal if I switch to Dolby Digital re-encoding as the player output instead. If the splitter can’t maintain “surround sound” for the amplifier setup, …

Remember, the splitter does NOTHING to or with protocols. It simply senses light on the input and drives light on the output.

Also, TOSLINK is one-way. HDMI is a communication bus, and negotiation goes on there, but the TOSLINK simply delivers the bits sent out by the source. The source side has an LED, and the destination side has a phototransistor. And I think the BD Player will output on the TOSLINK whatever encoding and bitrate is negotiated on the HDMI or set in the BD Player settings.

If the ReSound TV Streamer can interpret what the BD Player negotiates with the amplifier, and the splitter can keep up with the bitrate that results, it’ll work.

Also keep in mind that you should be able to set and limit the format and bitrate in the BD Player to what the amplifier, ReSound Streamer, and splitter can all handle. I would start out with a simpler format and then increase bitrate and encoding until it fails at either the amplifier or the ReSound TV Streamer.

@haggis said:

Also keep in mind that you should be able to set and limit the format and bitrate in the BD Player to what the amplifier

@haggis Thanks for the great advice. Unfortunately, perhaps the real cost of a $48 Blu-ray player special at Costco, is that for PCM downsampling there is no bitrate choice. The only options are “on” or “off.” Same for the dynamic range control option. The Yamaha HTR-5740 amplifier seems pretty sophisticated for its day - a 2004 purchase - and the manual says it can handle input at up to a 96 kHz sampling rate. On the input AUTO setting, it automatically decides what format it’s being sent and adjusts its decoding according. So we’ll see soon how it goes as the TOSLINK splitter is out for delivery.

One down side to using Toslink, at least in my case, was that when using optical, I can’t control the TV volume with the remote. My Samsung TV came with no audio output except optical, so I am stuck with it. Even with my lousy hearing, I could tell that the quality of audio out of the TV speakers was seriously lacking, and needed to go through my stereo amp.

I’m probably in need of more expert advice from @haggis. But the powered TOSLINK splitter works GREAT! The Samsung Blu-ray player is set to produce lossless PCM sound that can be automatically downsampled and is produced in Surround Compatible format. The Yamaha amplifier says it’s getting 6 channel sound from it’s TOSLINK branch and I’m getting great, VERY clear stereo from the ReSound TV Streamer 2 getting the other branch of the TOSLINK feed from the splitter.

The puzzle where Haggis might weigh in is the speech coming out of the Yamaha speakers is now clearer than ever. Not very careful, controlled experimentation here but two unsubstantiated thoughts come to mind. One is that I must have at least 10 to 12 feet of TOSLINK cable that I used originally to hook the Yamaha amplifier up to the digital audio out of the TV. And I never dusted the cable ends before. So now I have hooked this humongous length of cable from the TV up to the splitter, which is essentially a repeater and reamplifies the signal, I presume. And also on the cable end taken out of the amplifier, I blew it with compressed gas to chase away any fine dust that might have leaked into the connection over the past 11 years it was plugged into the amplifier (I also air-dusted off the TOSLINK port doors before making any new connection).

I read what Haggis said about digital transmission being all or none (same as over-the-air digital TV reception - a lot less sensitive to noise than good ol’ analog broadcasts). But I’m wondering whether the incredibly better sound that I’m getting now out of the amplifier and the speakers isn’t the result of the amping repeater function of the splitter and/or me dusting off the connector ends. Any advice from anyone on the care and feeding of optical connections is welcome.

Since all this “careful” experimentation is just based on watching the opening scenes of An Officer and a Gentleman (Blu-ray version), I probably should watch a bunch of other Netflix disc movies before I get too excited about the results. But so far, I’m really glad that I got the ReSound TV Streamer 2, the powered TOSLINK splitter, and actually went to the trouble of checking in what format the Samsung Blu-ray player was set to produce digital audio!

Edit_Update: What may be involved with the improved sound is the BEND RADIUS of my original very long TOSLINK cable. I didn’t pay attention to how and if I bent the cable to any significant extent (too much bending in the extreme can break the fiber optical path). When I pushed the amplifier back into its shelf, I may have caused the fiber to bend in a pretty abrupt 90 degree turn as the amplifier pushed up against the rear wall of the cabinet. Similarly with coiling up the rest of the excess cable behind the TV stand, there may have been one or two relatively abrupt U-turn bends, curved but of a relatively short turning radius. Reading blogs, depending on the nature of the (usually) plastic optic fiber in the TOSLINK cable, each cable has a “certified” bend radius, below which there is likely to be transmission loss internally as you try to reflect light around a bend while bouncing off the interior “walls” of the fiber. What I’ve read says that the allowable bend radius is usually > 1 to 1.5 inches. So now, rather than having any relatively abrupt bends, I have my excess cable length looped in big circles - I probably should get a much shorter length cable that can run relatively straight from TV to TOSLINK splitter. Again, what I’ve been reading agrees with Haggis’ pronouncement that transmission is usually ALL or NONE but perhaps with my previous cable kinks, I was closer to none than to all. And repeaters (such as the TOSLINK splitter has) are suggested as a fix for transmission problems over distance. So in setting up my TV streamer, I lucked out in buying a repeater to boost signal strength and I greatly unbent a much too long TOSLINK cable that I had unthinkingly twisted this way and that to stuff into a narrow space.

Another interesting tidbit that I read is that if there is transmission loss in Dolby Digital 5.1, transmission will shut down to protect your amplifier and speakers from reading corrupted data that is interpreted as “turn up the volume to the max.” But DD 5.1 is the low man on the codec quality totem pole. I wonder if PCM transmission shuts down in the same way from some internal checksum or such? My previous signal certainly sounded a bit degraded to what I hear now so I doubt PCM safeguards the audio setup in the same way that DD 5.1 is supposed to.

The following site has some pretty good, thorough explanations of Home Audio that might help other beginners like me: PCM Audio in Stereo and Home Theater11 (see further topics at bottom of article, for example).

Far you have come, young Padawan. No longer in need of my training, you are.

You hit the nail on the head on every point. I’m glad that splitter worked! Yes, it does act as a good repeater.

But speed of light being what it is and all, it shouldn’t really matter how long your TOSLINK is in the house as long as you restrict the bend radius, because you increase your losses from the loss of total-internal-reflection.

The better sound, if it’s qualitative, is probably more likely due to the idiosyncrasies of the encoding change. But it could have to do with signal quality and losses, because the DSP algorithms will attempt to reconstruct the signal if the reception is poor before it drops out altogether. Who knows?

PCM transmission is much simpler and easier to compensate for in DSP algorithms than DD 5.1, which has all kinds of sticky details in the encoding that must all be received for reproductions.

Looks like a good link. I’ve bookmarked it for future reference. I, myself, am a novice with the details of audio encoding/decoding but I’ve tried to use my general understanding of the physics and electronics to inform the debugging efforts.

Thanks for the feedback, Haggis. I tried the Dolby Digital 5.1 encoding from the Blu-ray player and PCM definitely seems of higher audio quality, speech is clearer. BTW, the online reviews of the 2013 Blu-ray release of An Officer and A Gentleman cite the disc for both the quality of its audio and its video with some quibbling here and there, such as heavy machinery scenes not having the full-throated roar that one would expect in real life from such equipment.

I might need a good Blu-ray test disc though. I’m not 100% sure that PCM in Surround Compatible mode does not just send the stereo sound to both front and back stereo speakers as the 5:1 sound. So I am open to recommendations from anyone on movies or test discs where one can hear distinctly different sounds on different channels all at the same time. I have a mid-2000’s test disc that I’ve used to confirm all my speakers are operating and are assigned to the right channel by the amplifier but that’s about it as to what the disc can do, AFAIK.

Thanks for confirming that. I was wondering, though, if I do that, how well the optical cable from the TOSLINK splitter would hold up if I frequently unplug and replug the TV Streamer 2 from the TV setup to move it over to use by my computer and then back again to the TV setup. I think ReSound would be smart to emulate Phonak and produce a less fancy streamer that, say, just had PCM functionality and fewer connection options, only cost $99 at Costco (like the Phonak). Then it would be more affordable to have a couple streamers scattered around the house hooked up to the different devices like computer and TV that one might want to stream from using AC power without wearing out Li-ion battery powered devices like the Phone Clip+ or the Multi Mic. Anyone’s comments on the durability of frequently unplugging/replugging TOSLINK devices would be welcome - I’d think the connectors would get a LOT more exposure to dust and dirt that way, too.