Re: New clock on satellite receiver
Hi, I have played with the idea. But my receiver is still in warranty and full of tiny SMD parts.......
I saw a 27 MHz canned crystal oscillator but I am not sure this is the one to tackle....
Also need a servicemanual....
MPEG sounds kind of funny.......
I don't believe the commercial talk that it is equal to CD quality......
FaZ72 said:
Hi, I have played with the idea. But my receiver is still in warranty and full of tiny SMD parts.......
I saw a 27 MHz canned crystal oscillator but I am not sure this is the one to tackle....
Also need a servicemanual....
MPEG sounds kind of funny.......
I don't believe the commercial talk that it is equal to CD quality......
Dynamic range is just a indicator for the resolution, so if its like an old cheap cassette deck, no way to make it hi-end. Jitter by itself at first limits low level resolution, so i see no sense to reduce jitter here, you only get a noise floor with improved noise...and i forgot to say: improving jitter on a dig-receiver = improving pll, because the sat downstream has its own timing and the receiver has to be synchronized to it; so the xo clock is only the reference for the dsp and its pll. Improving this is not easy, because the rf loc has a pll and the mpeg output is sync to another pll, on the data speed. here a fft of a musik transmission, see the max dynamic 130db, but in audio is only (20db max,-96db noise floor) about 76db in the 32k-fft, maybe about 50db effectiv. not much,eh ?
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Re: Re: New clock on satellite receiver
Most of the time, having digital audio is enough for them to write "CD quality" on the box...
Elso Kwak said:
Hi, I have played with the idea. But my receiver is still in warranty and full of tiny SMD parts.......
I saw a 27 MHz canned crystal oscillator but I am not sure this is the one to tackle....
Also need a servicemanual....
MPEG sounds kind of funny.......
I don't believe the commercial talk that it is equal to CD quality......
Most of the time, having digital audio is enough for them to write "CD quality" on the box...
Re: Re: Re: New clock on satellite receiver
With the state of CD mastering today, my kids Fisher Price cassette deck is "CD quality".
As for MPEG audio streams, this is probably going to be MPEG layer 2 (not MP3), which doesn't have the same complexity of filtering. On UK DVB broadcasts, I can quite clearly hear the compression artefacts in a 192k bitstream. By comparison, mp3 is very good at that rate. Listen for any form of audience noise e.g. clapping to really detect the nasty fluttering sounds instead of crisp claps. I've even heard FM broadcasts that have obviously been relayed from a compressed bitstream
The BBC really has gone downhill in recent years, and I'm not just talking about the programming...
Bricolo said:
With the state of CD mastering today, my kids Fisher Price cassette deck is "CD quality".
As for MPEG audio streams, this is probably going to be MPEG layer 2 (not MP3), which doesn't have the same complexity of filtering. On UK DVB broadcasts, I can quite clearly hear the compression artefacts in a 192k bitstream. By comparison, mp3 is very good at that rate. Listen for any form of audience noise e.g. clapping to really detect the nasty fluttering sounds instead of crisp claps. I've even heard FM broadcasts that have obviously been relayed from a compressed bitstream
The BBC really has gone downhill in recent years, and I'm not just talking about the programming...
But the point in not attaining audiophile quality from an mpeg2 stream. I beleive very few people on this forum (if any) think about that
The point is, since i am still listening to this signal, to improve it.
Connecting the receiver to a high-end dac realy makes a big improvement. The question is if, even improving the clock of the source changes the sound also
The point is, since i am still listening to this signal, to improve it.
Connecting the receiver to a high-end dac realy makes a big improvement. The question is if, even improving the clock of the source changes the sound also
Anyway, my humax reciever seems to be based on the Phillips SAA7215. This chip is the mpeg decoder and drives the SPDIF output aswell.
I read on the product information page:
- Single 27 or 40.5 MHz external clock for time base reference and internal processing. Internal system time base at 90 kHz can be synchronized via CPU port. All required decoding and presentation clocks are generated internally.
- Clock output 256 or 384 x fs for external DA converter or clock input; output can be set to high impedance mode.
Should it be possible to change the general 27/40.4 Mhz clock with a beter one to reduce jitter of the internal DAC and SPDIF output?
Thanks
I read on the product information page:
- Single 27 or 40.5 MHz external clock for time base reference and internal processing. Internal system time base at 90 kHz can be synchronized via CPU port. All required decoding and presentation clocks are generated internally.
- Clock output 256 or 384 x fs for external DA converter or clock input; output can be set to high impedance mode.
Should it be possible to change the general 27/40.4 Mhz clock with a beter one to reduce jitter of the internal DAC and SPDIF output?
Thanks
I am sure that there would be large sonic improvements if you could imrprove the clock. However, I think you will find this to be an extremely difficult project.
My understanding is that the satellite receiver box is analogous to the DAC box connected to a CD transport. That is, it will lock on to the signal sent to it. In this case the clock signal is embedded in the data stream coming from the satellite. So the real clock is in outer space where you don't have access to it.
All you can do is to try and improve the system (usually a PLL) that recovers the real clock. One trick that is commonly used for audio DACs is to use a VCXO instead of a PLL. However, this won't work for satellite receivers because a VCXO usually can only "pull" about 200 ppm or so. But many satellites have clocks with errors up to 5x this amount.
So I think you are left with trying to build the very best PLL circuit that you can. But this is not so easy as to install a pre-built clock module, and probably not worth the time and expense....
My understanding is that the satellite receiver box is analogous to the DAC box connected to a CD transport. That is, it will lock on to the signal sent to it. In this case the clock signal is embedded in the data stream coming from the satellite. So the real clock is in outer space where you don't have access to it.
All you can do is to try and improve the system (usually a PLL) that recovers the real clock. One trick that is commonly used for audio DACs is to use a VCXO instead of a PLL. However, this won't work for satellite receivers because a VCXO usually can only "pull" about 200 ppm or so. But many satellites have clocks with errors up to 5x this amount.
So I think you are left with trying to build the very best PLL circuit that you can. But this is not so easy as to install a pre-built clock module, and probably not worth the time and expense....
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