Anyone ever measured the sampling frequency of Modern TV optical output?

[srisaikat]

First pardon me if I am posting this in wrong section.

Recently I was toying with the optical output of my LG LED TV. Output was set as PCM. Now whatever the input I am providing with HDMI (source was Pioneer BDP and another DVD player) to the TV, I am getting only 48 KHz Audio sampling rate through the TV optical out as I can see it through Musical Fidelity M1 DAC.

The HDMI Audio out of both BDP and DVD player was set as RAW, so there was no scope of down-sampling. The optical output of my LG TV has only two options, "Auto" and "PCM". Under PCM there was no further sub-menu to select any particular sampling frequency. Naturally I have selected PCM as Optical output of my LG TV.

Now suppose I am spinning an Audio CD with either the BDP or DVDP, if I connect the digital output (SPDIF) directly to the DAC, I can see the sampling frequency as 44.1 KHz which is correct, but at the same time if I connect the TV Optical Out to the same DAC I am getting 48 KHz signal (as indicated by MF M1 DAC)

Please remember both the BDP or DVDP are same time connected to the TV through HDMI, from there to the DAC through Optical output of TV AND Directly to the DAC through COAX.

Making it simple through diagram.

BDP ----(HDMI)----> TV ---(Optical)----> DAC (48 KHz)
|
|____________ (COAX) --------> DAC (44.1 KHz)

I also tested with 88.2 and 96 KHz Audio files, result was same, if I connect the digital output (SPDIF) directly to the DAC, I can see the true sampling frequency which is 88.2 or 96 KHz, but at the same time if I connect the TV Optical Out to the same DAC I am getting only 48 KHz signal.

Any body have any clue which part of the chain limiting PCM audio signal to a fixed frequency? Is it the HDMI interface itself or the LG TV? As far I know HDMI can carry uncompressed multi-channel PCM signal, so stereo PCM audio signal is very well under it's limitation. My guess is LG TV here is the culprit? Any body tested or experienced such?

Please share your valuable reply.

 

[Fantastic]

The TV optical output must be 48Khz no matter what the input sampling rate is. Check the manual or on the Net. Nothing surprising, as they may have just designed it that way. Remember there will be a DSP chip inside the TV that can do this easily.

 

[elangoas]

The HDMI Audio out of both BDP and DVD player was set as RAW, so there was no scope of down-sampling. The optical output of my LG TV has only two options, "Auto" and "PCM". Under PCM there was no further sub-menu to select any particular sampling frequency. Naturally I have selected PCM as Optical output of my LG TV.

Have you tried "Auto" output on your TV's optical out?

 

[srisaikat]

The TV optical output must be 48Khz no matter what the input sampling rate is. Check the manual or on the Net. Nothing surprising, as they may have just designed it that way. Remember there will be a DSP chip inside the TV that can do this easily.

When a device have hdmi input and it have picture and sound output then obviously there is DSP inside. But question is, why should not it pass the original sample rate? Design wise or cost wise is it too hard?

Downsample, Upsample, Oversample, NOS whatever the math there it should be kept reserved for the downstream Device or Stand-alone DAC only. TV designer should not impose any limit on PCM audio sampling rate.

Have you tried "Auto" output on your TV's optical out?

Yes, I have tried with "Auto" settings too, it did not help to get original sampling rate. Still I get stuck to that 48 KHz.

Now my question is, will I get original sample rate with some other model or brand? Is there any premium model which do not have such limitation? Any body tested that feature with their Ultra priced model or brand? If you have spare time and option to check it then please report back here.

 

[Hari Iyer]

My VU TV when connected to my diy DAC displays 48KHz through optical connection.

 

[elangoas]

Yes, I have tried with "Auto" settings too, it did not help to get original sampling rate. Still I get stuck to that 48 KHz.

Now my question is, will I get original sample rate with some other model or brand? Is there any premium model which do not have such limitation? Any body tested that feature with their Ultra priced model or brand? If you have spare time and option to check it then please report back here.

Think so.. not so sure.. Any one using AVR with TV optical out, if they press info on the remote should display details of signal received 44.1 Khz or 48Khz..

 

[revanwrath]

Have you tried to use HDMI converter? I saw some of them that can get a stereo signal from a player up to 192kHz from HDMI input and split it into HDMI video + coax/spdif(toslink)/RCA(analog L/R) audio outputs. What are your experiences and thoughts about this?