Reflections and attenuators

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drmike

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Re: Reflections and attenuators
« Reply #200 on: 24 Mar 2019, 01:52 pm »
is the legato still available?
thank you.
drmike

art

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Re: Reflections and attenuators
« Reply #201 on: 25 Mar 2019, 05:21 pm »
We are going to make a limited number of the original version, with a lot of changes necessitated because some of the parts are no longer available. Plus, much better clocks.

We'll see how things go, and proceed from there. So, to directly answer your question, as of this moment, there are only 2 PCBs that have not been built. After that...............? We'll see.

art

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Re: Reflections and attenuators
« Reply #202 on: 25 Mar 2019, 05:39 pm »
I'm not sure what the critical jitter range is yet.  I have yet to see ANY correlation of jitter spectrum measurements to listening tests

That is probably because a.) no one has clocks good enough to make a difference, and b.) no one has the gear to measure what a really good clock is. We have both. And lots of data relating to it.


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The closest I have come to correlation is the jitter histogram that shows the distribution as well as the spectrum of the same.  I have seen some correlation there, but it's inconsistent.  When you have distribution, magnitude and spectrum all factoring in, it is hard to derive solid conclusions.  A LOT more study needs to be done in this area.

Ah, yes.....................the Wavecrest approach.................

We have one of those. TOTALLY useless when it comes to figuring out how any of this relates to what stuff sounds like. Really neat piece of gear, if you are into histograms. Not so much, once you try to relate that to the real world.

(We have some really expensive 10 MHz "reference oscillators", for our phase noise gear. They measure really poor, on the Wavecrest. It will show 2 peaks, like you have a source with correlated crap. The reason why is they are built with a 5 MHz rock, and they run that through a stage that clips, to pick off the 2nd harmonic. [5 MHz is better than 10 MHz, for lots of reasons, so that is how they make their 10 MHz units.] The drawback is the noise floor is higher than some of the competitors. But, those will not do -102 dBc @ 1 Hz. Which is needed, if you are trying to measure a really good clock. The ones with better noise floors have numbers at 1 Hz offset in the low 90s, and we have "$1 specials" that approach that level, so we use the one with a crappy noise floor. Great part, for our use. As long as you don't go by what the Wavecrest says, because it has a "camel" histogram.)

(OK..............I know you are probably wondering why that is. The positive and negative halves of the waveform are not symmetric, and that makes the Wavecrest goes nuts. It shows up on the + per and - per measurements.)

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My own DAC, by design, has no reclocker on the S/PDIF input.  Direct to the receiver.  The best DACs avoid reclocking on the inputs IMO, like the Metrum Acoustics DACs.  This way they get the benefit of truly low-jitter sources.

Kinda sorta defeats the purpose of having a low-jitter source! Yes, let's stick some generic clock, at a really high frequency (which may even be async!) in the chain.

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Using the optimum S/PDIF receiver is critical though.  They are not all the same.  Some of them can result in much lower jitter to the D/A, others are junk.

Yes, they are. We really hate the ones with Schmitt trigger inputs. Go stick one of those on you TDR. Think about what that energy being dumped back on the input does, on a TDR..........

art

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Re: Reflections and attenuators
« Reply #203 on: 25 Mar 2019, 05:52 pm »
They are 5X7mm surface-mount.  Can you deal with that?

Si. We have a test fixture, with a socket for those. Somewhere. I'll have to dig it out. Probably have not used it in at least 5 years.

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  I may be able to send you a SILABS 530CB49M1520DGR  - this is 49.1520MHz 3.3VDC  It may have solder on the pads.  Period jitter RMS spec 2psec. After my logic is added, 7-10 psec is the result.

OK.................!

I assume it uses the corner pads, and not the 2 in the middle, so I can use the same socket.

BTW, we measured one of their competitors. (It was for some Pro Audio company, and I forget who they were. Not that it matters, because I wouldn't tell who they are anyway.)

For some reason, they liked how they sounded. You could not pay me to use them. Let's just say the engineer that tried to get me involved on that project got canned! So, I have no idea what happened to them.

So, I am giving  you fair warning......................you may want to be really, really, really sure you want to see their phase noise.

BTW, are all of these parts 45/49 MHz, or are they 22/24 MHz ones? I need to stick a D flip-flop in the chain, instead of a inverting buffer, to drive the rig, if they are 45/49. Just need to know what chip needs to be in the drive part of the fixture. The only drawback is the noise floor will show up around 6 dB higher if we need to divide by 2, and tell the machine to reference it to the actual DUT frequency. When you do that, all it does is shift the entire plot up 6 dB. But, the real noise floor is really lower.

Since we do not care about noise floor, we don't care! You might.................

drmike

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Re: Reflections and attenuators
« Reply #204 on: 25 Mar 2019, 06:03 pm »
would it be better to wait for the new legato?
thanks,
drmike

art

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Re: Reflections and attenuators
« Reply #205 on: 25 Mar 2019, 06:12 pm »
That is the new Legato. The only question is whether or not we will make more than a small run or not.

audioengr

Re: Reflections and attenuators
« Reply #206 on: 25 Mar 2019, 08:23 pm »
Quote
Ah, yes.....................the Wavecrest approach.................

We have one of those. TOTALLY useless when it comes to figuring out how any of this relates to what stuff sounds like. Really neat piece of gear, if you are into histograms. Not so much, once you try to relate that to the real world.

(We have some really expensive 10 MHz "reference oscillators", for our phase noise gear. They measure really poor, on the Wavecrest. It will show 2 peaks, like you have a source with correlated crap. The reason why is they are built with a 5 MHz rock, and they run that through a stage that clips, to pick off the 2nd harmonic. [5 MHz is better than 10 MHz, for lots of reasons, so that is how they make their 10 MHz units.] The drawback is the noise floor is higher than some of the competitors. But, those will not do -102 dBc @ 1 Hz. Which is needed, if you are trying to measure a really good clock. The ones with better noise floors have numbers at 1 Hz offset in the low 90s, and we have "$1 specials" that approach that level, so we use the one with a crappy noise floor. Great part, for our use. As long as you don't go by what the Wavecrest says, because it has a "camel" histogram.)

(OK..............I know you are probably wondering why that is. The positive and negative halves of the waveform are not symmetric, and that makes the Wavecrest goes nuts. It shows up on the + per and - per measurements.)

I don't use a Wavecrest.  I use a 7GHz Tek scope with jitter measurement software on it.  When I get two humps, I fix the product so it only has one hump.


audioengr

Re: Reflections and attenuators
« Reply #207 on: 25 Mar 2019, 08:26 pm »
Quote
BTW, are all of these parts 45/49 MHz, or are they 22/24 MHz ones? I need to stick a D flip-flop in the chain, instead of a inverting buffer, to drive the rig, if they are 45/49. Just need to know what chip needs to be in the drive part of the fixture. The only drawback is the noise floor will show up around 6 dB higher if we need to divide by 2, and tell the machine to reference it to the actual DUT frequency. When you do that, all it does is shift the entire plot up 6 dB. But, the real noise floor is really lower.

That's a non-starter. The flip-flop will double the jitter.  Forget it.

art

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Re: Reflections and attenuators
« Reply #208 on: 25 Mar 2019, 09:04 pm »
NO IT WILL NOT!!!!

Did you not see the phase noise plot I posted in the USB thread? The jitter is a function of the BW over which it is measured. Which, in this case, is 1 Hz to 1 kHz. (Maybe you missed the part about how we feel the noise floor is pretty much meaningless.) It has nothing to do with the divider. All it does it lower the entire plot, and therefor the dBc value, by 6 dB. It does not effect the jitter.

If all that you do is measure the stinking noise floor, then, yes, the noise floor will come up, by around 2 dB, in some cases. I know, because I do this all day long.

I need something that will drive a 50R load (this is RF world), and it is the only difference is a picogate inverter or a picogate flip-flop. I have made enough of these plots to know how much the noise floor goes up, IF you have to insert an additional gate. (Sometimes I do that, on purpose, so I get it reference to 11.2896 MHz, for a specific situation, without s/w manipulation.)

But, whatever. I offered. Go ahead and measure the noise floor on your fancy 'scope (which works on pretty much the same method as the Wavecrest) and continue to wonder why you can not find a correlation between "jitter" and subjective listening tests. Good grief, man.

This is nothing personal, but this is what I refer to when "digital guys" ramble on about "jitter", compared to what the RF world calls "jitter". Which is really the phase noise, when you are talking about clocks, because that is how oscillators are characterized.

Yeah, I know......................"the spec sheet says".....................the spec sheet says diddly-squat because a bogus "jitter" number makes for a nice spec sheet and is real easy to measure. Other than that, it is meaningless, for digital audio.

Yeah, I know...............in timing, jitter means one thing. In audio, even though your fancy AP-1 (or -2 or whatever) gives a "jitter" number (which has its value, in its own right), it can not look at what goes on below 1 Hz. (It wasn't designed for that purpose.)

That is where it makes a difference. That can only be done by examining the phase noise of the clock. Which I have offered to do.

Without sending you a bill for $100 or so. (The gear to do that is not cheap, so it doesn't get done for free very often.)

Whatever.

audioengr

Re: Reflections and attenuators
« Reply #209 on: 25 Mar 2019, 11:07 pm »
NO IT WILL NOT!!!!

Did you not see the phase noise plot I posted in the USB thread? The jitter is a function of the BW over which it is measured. Which, in this case, is 1 Hz to 1 kHz. (Maybe you missed the part about how we feel the noise floor is pretty much meaningless.) It has nothing to do with the divider. All it does it lower the entire plot, and therefor the dBc value, by 6 dB. It does not effect the jitter.

If all that you do is measure the stinking noise floor, then, yes, the noise floor will come up, by around 2 dB, in some cases. I know, because I do this all day long.

I need something that will drive a 50R load (this is RF world), and it is the only difference is a picogate inverter or a picogate flip-flop. I have made enough of these plots to know how much the noise floor goes up, IF you have to insert an additional gate. (Sometimes I do that, on purpose, so I get it reference to 11.2896 MHz, for a specific situation, without s/w manipulation.)

But, whatever. I offered. Go ahead and measure the noise floor on your fancy 'scope (which works on pretty much the same method as the Wavecrest) and continue to wonder why you can not find a correlation between "jitter" and subjective listening tests. Good grief, man.

This is nothing personal, but this is what I refer to when "digital guys" ramble on about "jitter", compared to what the RF world calls "jitter". Which is really the phase noise, when you are talking about clocks, because that is how oscillators are characterized.

Yeah, I know......................"the spec sheet says".....................the spec sheet says diddly-squat because a bogus "jitter" number makes for a nice spec sheet and is real easy to measure. Other than that, it is meaningless, for digital audio.

Yeah, I know...............in timing, jitter means one thing. In audio, even though your fancy AP-1 (or -2 or whatever) gives a "jitter" number (which has its value, in its own right), it can not look at what goes on below 1 Hz. (It wasn't designed for that purpose.)

That is where it makes a difference. That can only be done by examining the phase noise of the clock. Which I have offered to do.

Without sending you a bill for $100 or so. (The gear to do that is not cheap, so it doesn't get done for free very often.)

Whatever.

We are not talking about clocks, we are talking about changing data in S/PDIF and I2S.

art

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Re: Reflections and attenuators
« Reply #210 on: 26 Mar 2019, 02:46 am »
Yeah, I got that..........................

Dude, you are at the quarter-pole. You got the length of the cable makes a difference, the RX stage makes a difference, and some other stuff right. Now you want to crap out when it comes to the clock, as you are heading down the stretch.

Why do you think the folks who buy our crap say "Wow, my digital system finally sounds just like my analog system!"?

It is a free country, which means no one can do your thinking for you. All I can do is give clues. Which, thankfully, 98% of the industry ignores. (Just wish the 2% that did would buy more parts from us!)

Whatever.