ARC Audio Quality

tinforme

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Jan 27, 2025
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Hi, I’m trying to track down the cause of some poor sound quality in my setup.

When using the Wiim Amp Pro as a streamer to play Spotify, the quality is, in my view, excellent.

However, the sound quality is not as good when feeding the Wiim Amp Pro from my TV. It seems slightly veiled by comparison.

In my setup, the source is an Apple TV, plugged into my TV via HDMI. The TV then outputs the audio to the Wiim Amp Pro via HDMI ARC.

The output levels of the two inputs initially did not match, with a measured difference of around 12dB at the same volume setting, but I was able to dial this out using the pre-gain settings in the Wiim app, +10 for the TV and -2 for the Ethernet input.

My testing scenario is comparing Spotify audio, with the same track, at the same level using the Spotify app on the Apple TV, compared to Spotify via the built-in Wiim streamer. In this scenario the built in streamer produces the better results.

The TV is using ARC (and does not support eARC) and is set to output PCM.

I have tried replacing the HDMI connection between the TV and the Wiim Amp Pro with an Optical connection, but this seemed to have the same performance as the HDMI.

I have also tried replacing the Apple TV as the source with a Chromecast, but if anything the quality was slightly worse.

I suppose I’m trying to figure out what could be responsible for the difference I’m hearing.

I imagine one candidate could be the TV, so I’ve been trying to understand what is happening in the audio chain. My understanding is that The Apple TV should be outputting multichannel PCM, and the TV down-mixing it to stereo PCM.

With this in mind, I changed the audio settings in the Apple TV from Auto (LPCM) to Dolby Digital, which sounded much worse, and then to Stereo, which I think may have made some slight improvement to the sound, although this was pretty marginal if any.

So my question now is what could the TV be doing to the signal? I’m suspicious that it is not passing it through unaltered, even though the input and output are both stereo PCM. To add further to this theory, the Wiim app reports the same audio format wether I am listening to output from the TV’s own content, or from the Apple TV. I note that some newer TVs have options such as “Pass-through” as well as PCM, which would imply such a difference also.


Is there anyway I can confirm this theory that the TV is impacting the audio quality, short of getting hold of a different one? I’ve seen devices such as HDMI splitters, but I’m not familiar with these and I’m not sure if they could be useful in troubleshooting this scenario.

I guess there are two theoretical ideal chains - Apple TV outputs multichannel LPCM, a TV passes this through unaltered to Wiim Amp Pro, but I’m not sure if the Wiim Amp Pro can decode this? The other chain would be the Apple TV is set to output Stereo PCM, which is passed through unaltered by the TV to the Wiim Amp Pro, but it seems my TV at least is not exactly doing this. I’m not sure if other TVs are on the market which do allow pass-through of Stereo PCM over ARC?

It would be great to get any opinions on what could be causing this quality difference, and possibly how it could be addressed. If it’s not the TV, is is perhaps a configuration issue, or is the signal path meaningfully different when feeding the Wiim Amp Pro from the Digital inputs vs using the Ethernet source?

As a note, when searching before posting this issue, I have seen one other report of this issue on the forum, albeit with a much newer Samsung TV, below:https://forum.wiimhome.com/threads/samsung-tv.3027/
 
Welcome.

The tv itself does seem to be the consistent factor here regardless of output (hdmi / optical).
I don't see an hdmi splitter making any difference as the signal is already out of the tv by then.
 
Thanks :)

Yes I think so. That's a good point, and I'm very much thinking out loud on that front. Sort of musing if there may be a product that sits after the Apple TV and could send ARC audio to the Wiim, and send at least a video signal to the TV, also retaining CEC controls. Such a setup if it exists would take the TV out of the audio loop, with the hypothetical device performing the audio passthrough over ARC. But it's all slightly inelegant.

In the meanwhile I had the thought of perhaps trying to get my hands on another optical source, and see if I can rule out the issue being with the digital inputs on the Wiim.
 
I don't think TV can be considered a serious audio source. TV audio generally isn't that high resolution wise. It may be multi channel but only 16bit/48kHz which is DVD quality.
 
I guess there are two theoretical ideal chains - Apple TV outputs multichannel LPCM, a TV passes this through unaltered to Wiim Amp Pro, but I’m not sure if the Wiim Amp Pro can decode this?
No, it cannot decode multi-channel LPCM (at least not according to the specs, I did not and I cannot test this), just multi-channel Dolby Digital (AC3).

Some TVs have an explicit "pass-through" setting. If yours does, that would be your best bet to pass on 2 channel LPCM unaltered from the Apple TV to the WiiM Amp Pro.
 
I don't think TV can be considered a serious audio source. TV audio generally isn't that high resolution wise. It may be multi channel but only 16bit/48kHz which is DVD quality.
Ah! In this case the ultimate source is the Apple TV, with my TV set only being in the loop to feed the Wiim an HDMI ARC signal.
 
Just wanted to give a bit of an update as I've been fairly into the weeds on this one!

I had a message suggesting to explore EQ'ing out the difference, which inspired to me take some sound recordings and bring them into Audacity for visualisation with a spectrogram, to see if I could quantify the nature of the qualiy issue I was seeing, but also to check that I'm not just imagining the difference. I do find it quite noticable, but the placebo effect is a powerful thing, especially when it comes to audio. Of course the caveats here are that I'm just recording on an iPhone microphone, albeit losslessly, and my room, and speakers, and whatever background noise is present, are very much in play, so it's possible these factors overwhelm any differences in the sources.

With that said, I used my original two sources of Spotify Premium via the Streamer in the Wiim Amp Pro, and via the Spotify app on the Apple TV via HDMI, for comparison.

I also included a PS3 to serve as an alternate source with a physical CD with the same track, so I could feed the Wiim with Optical directly, bypassing the TV, and also experimented with connecting the PS3 by means of the TV via HDMI.

Long story short, with subjective listening the PS3 with a CD via optical sounded great, as did the Spotify Premium directly via the Streamer. Anything involving the TV with HDMI caused a dramatic reduction in sound quality.

When viewing the spectrograms, the differences were subtle, but the other setups showed a slightly more noticable range of artifacts, such as compressed frequency ranges, and unexpected treble boosts. I'm not overly confident in the quality of these recordings, and even less confident in my ability to analyse them, but they were enough to confirm that "something" audible and consistent is being done to the signal, which is all I was really after.

At this point, I was able to get great audio from the Wiim streamer, and the PS3 via the Wiim's optical input. Which leaves the possible sources of the problem as the TV, the HDMI input on the Wiim, or the Apple TV itself.

With this in mind, I grabbed a bargain HDMI audio extractor from eBay, with an optical output. The plan here was to place this between the Apple TV and the Wiim, to route the audio directly without involving the TV, which could rule out the Apple TV as the problem device.

With the HDMI to optical audio extractor in place, the Apple TV sounded great, a huge difference. This is pretty much a viable solution to the sound quality issue, and I've very impressed with what is a very cost-effective device. In this scenario, I prefer the output with the Apple TV set to Auto, rather than to Stereo.

There are a couple of notable things about this approach which may be of interest to anyone experiencing a similar issue.

With the TV in the audio loop, outputting either HDMI or Optical, the levels were much quieter vs the other Wiim inputs. With this extractor providing audio via optical, this level difference is no longer noticable, that is, it's a much louder source than via the TV. I've seen several people mention the Wiim HDMI input being quiet and requiring a large pre-gain, and whilst this setup is not using HDMI, it is making me suspect that the TVs themselves may possibly be the cause of this level imbalance, given the change I've observed via optical.

Secondly, I've also been testing with Apple Music lossless. I can't tell any difference between this and Spotify Premium, but I have noticed that some Apple Music tracks will show up on the Wiim Optical input as 44.1kHz and some as 48kHz, whereas before everything coming over optical via my TV was 48kHz. This would lead me to suspect that extractor is faithfully passing on whatever audio input it recieves, whereas the TV was resampling it.

Of course, having the extractor in the loop is not ideal - it can only handle a single source, it requires additional cabling, and in my case, as it is powered by the TV USB port which is only powered when the TV is on, it is preventing the Apple TV waking the TV up with a single remote. I have left in place the HDMI ARC cable between the Wiim and the TV to allow volume control to continnue to work via CEC, but this does mean the Wiim will swap to the HDMI input for audio when turned on.

At this point, although my sound issue is basically cured, I'm simply curious about the cause of the issue, and there are two remaining culprits - the TV or the HDMI input on the WiiM amp. Whilst at this point I'm exceedling suspicious of the TV, it would be nice to confirm. To track this down, after some reading I'm planning to source an ARC HDMI audio extractor. This will perform a similar function to the extractor mentioned above, but will output audio to the Wiim over HDMI via ARC, rather than optical. If this setup sounds good, then the perpetrator was the TV, in the living room, with the HDMI cable, all along. To be continued!

If anyone got this far - thanks for reading! :)
 
Well, the aforementioned ARC audio extrator arrived! And I'm pleased to report than when it's in the audio chain instead of the TV, the sound quality over HDMI ARC is excellent. So I think it's fair to say that in my opinion the TV was introducing the audio quality issue, and there is no issue with the digital inputs on the Wiim.

To follow up on two through-lines of the investigation so far, the levels from the ARC extractor are much higher again than from the TV, so I have been able to dial out the large pre-gain which was needed when the TV was in the loop. Also, I can see that the sample rate being fed into the Wiim is following the sample rate of the content, which would lead me to assume that the ARC extractor is likely not resampling nor otherwise altering the audio signal on the way through, which is ideal, and in contrast to the TV.

Whilst both the extractors sounded great, going forward I'll likely stick with the ARC extractor as it has one cable fewer, avoiding the optical connection, and the associated input swapping in the app when powering up. There are currently a couple of minor CEC-related quirks, but nothing prohibitive, and could be user error on my part as I'm just newly configuring the device.

One oddity I noticed when looking at the spectrograms in this setup is that when the Apple TV output is Auto, there is some (unwanted) treble boost, which mostly goes away when set to Stereo. Bizarrely, when I had the optical extractor in the chain, this was the precise distortion which appeared when the Apple TV was set to Stereo, and went away when set to Auto, so the behaviour appears to be reversed. I currently have no explanation for this, neither for what could be introducing distortion of this kind in the first place, nor for why changing the Apple TV settings would have an impact.

But in summary, for anyone in a similar situation with poor quality or quiet audio output from their TV, introducing an ARC extractor might be a viable workaround to restore excellent sound quality. And for those with an Apple TV, choosing Stereo output would appear to give the best results.

Of course, the ideal solution, as identified by harkpabst above, would be if the TV was able to passthrough stereo unaltered, but sadly mine doesn't seem to do so. Perhaps an investment for another day 😅
 
Thanks :)

Yes I think so. That's a good point, and I'm very much thinking out loud on that front. Sort of musing if there may be a product that sits after the Apple TV and could send ARC audio to the Wiim, and send at least a video signal to the TV, also retaining CEC controls. Such a setup if it exists would take the TV out of the audio loop, with the hypothetical device performing the audio passthrough over ARC. But it's all slightly inelegant.

In the meanwhile I had the thought of perhaps trying to get my hands on another optical source, and see if I can rule out the issue being with the digital inputs on th
Hello tinforme, thank you very much for the detailed description. I'm currently facing the same challenge. Can you perhaps add which arc Audioextractor you are using and how you have wired the individual components?
Many thanks in advance
 
With hdmi extractor in the loop can you change volume via tv remote? If so how are you connecting it and can you provide a link to it if i would like to buy it.
 
Hello tinforme, thank you very much for the detailed description. I'm currently facing the same challenge. Can you perhaps add which arc Audioextractor you are using and how you have wired the individual components?
Many thanks in advance

Yes, certainly. It's a FeinTech AX310. It's the only ARC audio extractor I've used, so I'm not really in a position to make a recommendation per se, but so far so good.

I'm using the Apple TV as a source, this is connected via HDMI to the Input of the extractor.

Then there is a second HDMI cable running between the "TV eARC" output of the extractor and the "ARC HDMI" port on my TV. This carries the video signal from the extractor to the TV. This same connection also transports an audio signal from the TV to the extractor so sound is also available from other sources plugged into the TV, and from the TV itself. Note that this audio will presumably be subject to any processing or other audio output issues the TV introduces. Choosing the ARC port on the TV also ensures the CEC commands can be transmitted between the Apple TV, the TV, and the Wiim, for controlling volume with a single remote.

Finally, there is a third HDMI cable running from the "Soundbar eARC" output of the extract to the ARC HDMI input on the Wiim Amp Pro, which carries the audio to the Wiim.

I operate the unit with "eARC" mode on, otherwise I don't get any sound output from any source when connected as above. The device manual would suggest this mode will play audio from the TV and not from the source, however if I set the TV to output to an unused optical port, and not the HDMI ARC output, I still get audio, presumably directly from the source. So my current understanding based on my observations is that in this mode the extractor can present audio from the TV and from the source, and not just from the TV, despite the manual's description. I have not verified this with the manufacturer and theoretically there is a chance it's just round-tripping the audio through the TV, but given my observations of the sound quality and the sample rate, and the fact that I disabled HDMI Audio out on my TV while testing, I think that is not the case. Both my TV and the Wiim support ARC, and neither eARC, however this seems to work fine.

With hdmi extractor in the loop can you change volume via tv remote? If so how are you connecting it and can you provide a link to it if i would like to buy it.

Yes, when connected as above I can control the volume with the TV remote. I can also control the Wiim volume with the Apple TV remote, although the Apple TV remote will not bring up TV's volume control to display onscreen, so I have turned on the volume indicator on the Apple TV.

Please see below for the link, I believe it can also be purchased from outside of Germany / EU / Switzerland from Amazon DE (Amazon Germany).

I hope that helps you both! If you had both been having the same issue I had, it would be much appreciated if you'd be interested in contributing to the poll I'm trying to start to track this problem, link below, many thanks.

 
Many thanks for your help. I'll be happy to take a look at the links and will also try to implement your workaround for myself.
 
Many thanks for your help. I'll be happy to take a look at the links and will also try to implement your workaround for myself.
You're very welcome, and I look forward to hearing how it goes.

Can you tell us which TV model you’re using (so I won’t accidentally buy it)?

Are you sure? Because if you'd like to buy my actual TV, I'm open to offers :)

The TV model is in the other thread I linked just a couple of posts above. It's quite a few years old now so probably little risk of stumbling across one! To be fair it's a great TV generally. In fact, my current working theory is that every TV on the market may be resampling audio in the same configuration (stereo feed via ARC). If anyone think's that's a wild position, I'd invite them to prove me wrong by completing the quick test I've described in that thread - I'd be delighted to be wrong on this.

Whether the resampling alone results in an audible difference, or whether it points to the possibility of other processing being performed which could have an audible difference, are both different questions, but I think it's an interesting aspect nevertheless.
 
In fact, my current working theory is that every TV on the market may be resampling audio in the same configuration (stereo feed via ARC). If anyone think's that's a wild position, I'd invite them to prove me wrong by completing the quick test I've described in that thread - I'd be delighted to be wrong on this.
I won't bet against this for sure. :)
 
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