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The opposite of an attenuator?

John Phillips said:
From what I read, the TV PCM output level seems to be completely mad.

For the M30, 775 mV sensitivity for 106 dB SPL (what I assume from the spec. and seems OK to me) is equivalent to 2 V (full DAC output) for a deafening 114 dB SPL (nominal). If you can't get enough volume when the DAC volume control is fully up it looks like the TV sound average level may be a massive 48 dB down from full scale, or more. That's equivalent to a digital shift-down of a full 8 bits. That looks like a lot for an amplifier to fix, even partially.

I assume connecting another digital source to the DAC gives good volume levels when the DAC volume control is turned down - although I note your "Chief problem source" which makes this less clear. But if so, it seems the fundamental problem is with the TV or what the DAC sees from the TV over the digital audio interface (TOSLINK I assume).

What is the TV doing? Does the TV digital audio output level follow the TV's internal volume control so you see the combined effect of both controls?

Is the DAC somehow seeing only 8 bits of digital audio from the TV and interpreting these as the bottom 8 bits of 16-bit digital audio when it should see them as the top 8 bits? Is the TV putting out 16 pit PCM but the DAC is interpreting that as 24 bit PCM with zeros at the top? Is there a TV menu setting for the digital output that you can share that may shed some light? Is there any DAC input setting that may matter?

These thoughts all seem mad to me but something needs to explain the magnitude of what is being heard. Or have I got the situation wrong?
Click to expand...

You have the situation bang on. Although my other digital source, a pi running Kodi also comes up a bit quiet, although not so severely. I have dug through the TV config settings and cannot find anything to change the gain on the optical pcm output. Bit annoying, as we use the 4k chromecast on the telly for Spotify in this room.

Tried popping a Quad 34 pre-amp in between the DAC and m30s and I can get more volume. I’m thinking a simple active pre hidden away at a fixed volume may be the be the easiest answer here.
 
John Phillips said:
From what I read, the TV PCM output level seems to be completely mad.

Is the DAC somehow seeing only 8 bits of digital audio from the TV and interpreting these as the bottom 8 bits of 16-bit digital audio when it should see them as the top 8 bits? Is the TV putting out 16 pit PCM but the DAC is interpreting that as 24 bit PCM with zeros at the top? Is there a TV menu setting for the digital output that you can share that may shed some light? Is there any DAC input setting that may matter?
Click to expand...

My (limited) experience with TV spdif output is that it shows up as 20bit for stereo. (Not 24 or 16) I suspect this may go with TV/video now also trying to accomodate 'surround sound' source material and duly scaling the contributions to lower levels when trying to ''fit' into 2-channel output. As a result when we play files from iplayer their sound level is clearly higher than from broadcast via TV RX. (Only have Freeview FWIW, not sat or net TV.)
 
Jim Audiomisc said:
My (limited) experience with TV spdif output is that it shows up as 20bit for stereo. (Not 24 or 16) I suspect this may go with TV/video now also trying to accomodate 'surround sound' source material and duly scaling the contributions to lower levels when trying to ''fit' into 2-channel output. As a result when we play files from iplayer their sound level is clearly higher than from broadcast via TV RX. (Only have Freeview FWIW, not sat or net TV.)
Click to expand...
Yes. AIUI, the SPDIF/TOSLINK frame structure formally has 20 bits for an audio sample. A 16-bit sample is zero-padded at the bottom to fit exactly so I assume it will be seen as 20 bits. But there are also four extra bits for signalling that a consumer interface does not use; and I think these get used to extend the data to 24 bits.

Given the very low level of the TV output that @foxwelljsly sees, I can only think of a strange interoperability problem provided it isn't the TV attenuating the signal, such as mis-aligning the bits on the interface (which I have not heard of before). Very strange indeed.
 
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