Digital to analogue audio conversion problem - AVS Forum
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post #1 of 15 Old 05-11-2014, 03:14 AM - Thread Starter
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Hi folks, I am hoping someone here may have a solution or an explanation for a problem I am experiencing with what should be a very simple setup, trying to get the audio of my Tv to play through my stereo system.
E
The Tv is a Kogan unit with Coaxial Audio out. The stereo amp is a Denon DM39 with RCA analogue in. (It also has optical Toslink audio in, but I am using this to stream music from my laptop via Apple Airport Express).

I bought a digital to analogue converter, & connected the coaxial audio out from the Tv to it, & the RCA audio leads from stereo amp to it too.

So far so good. It worked as expected & I was happy....... BUT ....... Since my initial success I have found that whilst about 70% of the tv channels sound great through my stereo system, around 30% only produce a continuous reverberating noise. These same channels are perfectly fine when listened to through just the tv alone. All channels are digital broadcasts.

Any thoughts please?

Thanks,
Cuppa
Vic, Australia.
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post #2 of 15 Old 05-11-2014, 06:48 AM
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Couple things.

Quick guess the channels that produce noise could be Dolby digital

1. Does the DAC decode Dolby Digital? What make/model do you have.
2. If it doesn't you will need to the digital output to PCM

It looks like this is an option in the setup menu of the display.
From the manual
SPDIF Mode
This is used to select "SPDIF Mode" .This option is only used in HDMI\DTV mode.
1. Press / key to select "SPDIF Mode" option.
2. Press / key to select "RAW" or "PCM".

I'd try the settings above and see if this resolves the issue.

Report back and let us know.
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post #3 of 15 Old 05-11-2014, 07:12 AM
 
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Quote:
Originally Posted by trans_lux View Post

Couple things.

Quick guess the channels that produce noise could be Dolby digital

1. Does the DAC decode Dolby Digital? What make/model do you have.
2. If it doesn't you will need to the digital output to PCM

It looks like this is an option in the setup menu of the display.
From the manual
SPDIF Mode
This is used to select "SPDIF Mode" .This option is only used in HDMI\DTV mode.
1. Press / key to select "SPDIF Mode" option.
2. Press / key to select "RAW" or "PCM".

I'd try the settings above and see if this resolves the issue.

Report back and let us know.


Dolby Digital formats have an intrinsic 2.1 mix down. The Denon, if set to 'auto-signal' detection will make the appropriate discernment, etc. He should firstly check to see if his Denon is configured as I just mentioned. If not, he should do so. If it is, then you / 'trans' may be on to something. It's always wise to walk through all the set up menus that are available that can have an affect on the signal chain.

 

Either way, please send us the make and model of your unit - if we have that, you should get a quick and accurate path to follow...

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post #4 of 15 Old 05-11-2014, 09:18 AM
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The Denon he is using only has an analog input available as he is using the only dig input for an Apple Airport Express.
Settings should be performed in the display.


http://www.denon.co.uk/uk/product/pages/product-detail.aspx?catid=systems&subid=minimicro&productid=dm39dab
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post #5 of 15 Old 05-11-2014, 09:06 PM
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Quote:
Originally Posted by trans_lux View Post

Couple things.

Quick guess the channels that produce noise could be Dolby digital

1. Does the DAC decode Dolby Digital? What make/model do you have.
2. If it doesn't you will need to the digital output to PCM

It looks like this is an option in the setup menu of the display.
From the manual
SPDIF Mode
This is used to select "SPDIF Mode" .This option is only used in HDMI\DTV mode.
1. Press / key to select "SPDIF Mode" option.
2. Press / key to select "RAW" or "PCM".

I'd try the settings above and see if this resolves the issue.

Report back and let us know.

I agree. Set the TV's spdif mode to PCM and the problem should be solved.
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post #6 of 15 Old 05-12-2014, 04:24 AM - Thread Starter
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Hi folks,

Thanks for your replies. Unfortunately they have not helped yet.

 

Kogan sell a variety of different TVs which I understand are sourced from a variety of manufacturers & badged under the Kogan name. The model of my one is the KGN1080P32VAA  (need to enter model number in manual search box). I have searched the manual & the on screen options & found zero mention of SPDIF, RAW or PCM (not that I have a clue what any of those things are). 

 

Info on the digital to analogue converter I have makes no mention of Dolby.

 

Denon amplifier is RCD-M39

 

I guess it’s looking like either I have an icompatible DAC or simply that the TV I have is not configurable enough to do what I want.

 

It has been suggested to me that another possibility is that the channels on which I only get noise might be those which were digital prior to the full change over of all channels to digital 12 months or so ago, which might be nonsense??? As I said previously, all work ok on TV only.

 

If it is useful I can detail which channels are problematic.

 

Keeping my fingers crossed but with fading hope.

 

Regards

Cuppa

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post #7 of 15 Old 05-12-2014, 05:58 AM
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This should solve your issues.
http://www.gefen.com/gefentv/gtvproduct.jsp?prod_id=5980
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post #8 of 15 Old 05-12-2014, 06:20 PM - Thread Starter
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Thanks trans_lux. So it’s a Dolby issue then. Will have to save my shekels to buy as you suggest. 

 

regards

Cuppa

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post #9 of 15 Old 05-12-2014, 07:11 PM
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How do you receive your TV signal? If through a set top box, you may be able to set it to output PCM instead of DD 5.1. (Also, it seems unlikely that your TV can't be set to output stereo PCM since not all receivers can decode DD 5.1.)

Of course, all of this discussion assumes that the problem is the result of the tv sending Dolby to a DAC that can't decode it. That's a reasonable assumption, but it may not be the case as there's been no description from the OP about the channels that produce noise through the DAC.
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post #10 of 15 Old 05-12-2014, 09:02 PM - Thread Starter
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Quote:
Originally Posted by BIslander View Post

How do you receive your TV signal? If through a set top box, you may be able to set it to output PCM instead of DD 5.1. (Also, it seems unlikely that your TV can't be set to output stereo PCM since not all receivers can decode DD 5.1.)

Of course, all of this discussion assumes that the problem is the result of the tv sending Dolby to a DAC that can't decode it. That's a reasonable assumption, but it may not be the case as there's been no description from the OP about the channels that produce noise through the DAC.

Hi BIslander,

What further info about the channels that produce noise would be useful? (I’m not very knowedgeable about these things but could try to find out). The Gefentv DAC is Aus$140 here, more than I’d like to pay without first being certain it will resolve the issue. 

 

Tv signal requires no set top box, just an external antenna (with a mains powered signal booster). As I understand it all TV signals here are now digital, & most Tv’s sold in the past few years have not required a set top box. I have no settings to configure audio out. The Antenna recommended for our area is like this & ours looks almost identical. (We only moved here a few weeks ago ... so ‘inherited’ the existing antenna). 

 

Is the type of noise produced likely to be diagnostic? If so I could record it & upload it to youtube or similar & post a link to it here. 

 

Thanks

Cuppa

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post #11 of 15 Old 05-13-2014, 05:55 AM
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Your TV should tell you the type of audio it is getting on each channel. If the problem is the lack of DD decoding in the DAC, then you should get bad audio on channels with DD soundtracks and good audio on channels with stereo PCM soundtracks.
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post #12 of 15 Old 05-13-2014, 06:12 AM - Thread Starter
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As suggested by BIslander the TV does indeed tell me the type of audio it is getting, I hadn’t previously noticed it. Channels are either SD or HD with Dolby. translux was spot on, the problematic channels are indeed the ones with HD Dolby. I think the problem has been defined along with the solution. I thank you all for your help. Forums are great.

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post #13 of 15 Old 05-13-2014, 06:40 AM
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The manual for your TV says there's an analog audio output. p6 and p10 of the manual both identify the upper AV jacks to the left of the coax output as AV Out. Have you tried connecting that output to your Denon?
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post #14 of 15 Old 05-13-2014, 07:07 AM - Thread Starter
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BIslander - you are brilliant!  I had previously unsuccessfully tried plugging into the RCA AV out on the Tv, but the labeling on the rear of the tv had me thinking that the AV in was the AV out & vice versa. (Upper = outer.... not inner as I had thought). Your post had me check again & bingo! I now have all channels through my speakers. Thank you so much for bothering to take the time to look at the manual & post again, I really appreciate it, even though I feel pretty stupid about both my mix up and buying a DAC & coax audio cable I didn’t need. 

 

regards

Cuppa

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post #15 of 15 Old 05-13-2014, 07:10 AM
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Glad to help. Enjoy.
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