Jitter for duffers

andyjm

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A number of discussions that have referenced jitter. Some background for anyone who cares.

Picture yourself clapping along with a piece of music. Generally you clap in time with the beat, sometimes a little early, sometimes a little late.

If you think of the music beat as the ideal clock, and your clapping as the actual clock, then the differences between the two is the jitter. On average, your clapping is in time, but it may deviate from the correct beat in a random way. The technical term for this is phase jitter - the actual clock is the right frequency, but doesn't always tick at exactly the right time.

DACs can suffer from jitter in two ways:

1. In a synchronous system, the clock tick is the point at which data is considered valid. So for a S/PDIF data stream, every time the clock ticks the DAC looks at the S/PDIF data line and notes whether it is 1 or 0. If the clock has jitter, it is possible that the DAC looks at the S/PDIF data too early or too late and reads the data in error. These days, S/PDIF data rates are considered slow, and there is no system I know of that has so much clock jitter that data is read in error.

2. In a digital audio system, the clock tick is the point at which the audio sampled by the A2D converter. Implict in the process is that the clock ticks in the same regular way when the samples are played back by the DAC. If the clock used for the playback ticks slightly early or late (it has jitter) then the samples are played back slightly early or late and lead to distortion in the output signal. This is how jitter can effect the audio quality of the DAC output.

As jitter is a random process, its frequency / probability distribution impacts how audible it is. There is no standard way of reporting jitter, and it gets reported in different ways. I have seen peak jitter, average jitter, RMS jitter all reported - these figures are not comparable.

There have been a number of studies about the point jitter becomes audible, but no real consensus in academic papers. There have also been suggestions that jitter correlated to the audio signal is much more detectable than jitter that is purely random.
 

Blacksabbath25

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Sep 20, 2015
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andyjm said:
A number of discussions that have referenced jitter. Some background for anyone who cares.

Picture yourself clapping along with a piece of music. Generally you clap in time with the beat, sometimes a little early, sometimes a little late.

If you think of the music beat as the ideal clock, and your clapping as the actual clock, then the differences between the two is the jitter. On average, your clapping is in time, but it may deviate from the correct beat in a random way. The technical term for this is phase jitter - the actual clock is the right frequency, but doesn't always tick at exactly the right time.

DACs can suffer from jitter in two ways:

1. In a synchronous system, the clock tick is the point at which data is considered valid. So for a S/PDIF data stream, every time the clock ticks the DAC looks at the S/PDIF data line and notes whether it is 1 or 0. If the clock has jitter, it is possible that the DAC looks at the S/PDIF data too early or too late and reads the data in error. These days, S/PDIF data rates are considered slow, and there is no system I know of that has so much clock jitter that data is read in error.

2. In a digital audio system, the clock tick is the point at which the audio sampled by the A2D converter. Implict in the process is that the clock ticks in the same regular way when the samples are played back by the DAC. If the clock used for the playback ticks slightly early or late (it has jitter) then the samples are played back slightly early or late and lead to distortion in the output signal. This is how jitter can effect the audio quality of the DAC output.

As jitter is a random process, its frequency / probability distribution impacts how audible it is. There is no standard way of reporting jitter, and it gets reported in different ways. I have seen peak jitter, average jitter, RMS jitter all reported - these figures are not comparable.

There have been a number of studies about the point jitter becomes audible, but no real consensus in academic papers. There have also been suggestions that jitter correlated to the audio signal is much more detectable than jitter that is purely random.
interesting

Do you think that there are sound differences between CD players and Dacs that some are better managing the jitter better then others so you hear a difference in sound quality because of the jitter management ?
 

athegn1

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When I heard about jitter I searched and found this post:-

https://hydrogenaud.io/index.php/topic,109948.0.html

I then relaxed knowing that, as my setup is digital only, I live in an audible jitter free world.
 

Blacksabbath25

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Sep 20, 2015
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athegn1 said:
When I heard about jitter I searched and found this post:-

https://hydrogenaud.io/index.php/topic,109948.0.html

I then relaxed knowing that, as my setup is digital only, I live in an audible jitter free world.
what have you got a streamer ?
 

Blacksabbath25

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athegn1 said:
Phone and Chromecast Audio.
that’s a good one because I am not sure if there is some kind of Dac involved so no jitter as such because there would of been jitter in the recorded end like the recording studio .

but see your point *smile*
 

Andrewjvt

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MajorFubar said:
chebby said:
Yeah I always smile at the simpletons who think all this stuff is new.
There is nothing quite as good sounding as pure, clean, usb isolated, triple linear powered digital signal.

Even better when you place your dac ontop of speaker isolation products.

Can even change the original recording to conquer the loudness wars, I believe.

Takes a ruthlessly revealing system and makes it less so apparently.
 

chebby

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Blacksabbath25 said:
Wow that report was from 1974 so we are looking at vinyl then which I didn’t think suffered from Jitter I thought it was just a digital thing
The clue is in the name ‘BBC’. They broadcast digital sound and vision from very early on. It wasn’t about vinyl.

For instance, BBC FM radio was being distributed from broadcasting house - via dedicated GPO land lines - to every UK radio transmitter in 13 bit digital from the mid 1970s onwards. (Edit: actually from 1972 onwards which marked the start of the roll-out.) It only became analogue for the last few miles from the transmitter to your radio.
 

Blacksabbath25

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chebby said:
Blacksabbath25 said:
Wow that report was from 1974 so we are looking at vinyl then which I didn’t think suffered from Jitter I thought it was just a digital thing
The clue is in the name ‘BBC’. They broadcast digital sound and vision from very early on. It wasn’t about vinyl.

For instance, BBC FM radio was being distributed from broadcasting house - via dedicated GPO land lines - to every UK radio transmitter in 13 bit digital from the mid 1970s onwards. (Edit: actually from 1972 onwards which marked the start of the roll-out.) It only became analogue for the last few miles from the transmitter to your radio.
I didn’t realise

was there any connection between the BBC and Philips and Sony in the development of the CD player ?
 

chebby

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MajorFubar said:
chebby said:
Yeah I always smile at the simpletons who think all this stuff is new.
LOL.

It reminds me of teens who think the world of computers belongs to the young, so forgetting/ignoring that it was their great grandparent’s generation who developed it all! (The beginnings of the Internet date from the early 1960s and even the World Wide Web is 30 next year.)
 

MajorFubar

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Blacksabbath, digital audio substantially predates the invention of CDs. As Chebby said, for a start it was used to deliver radio to FM transmitters from at least as early as 1972. Probably lots of other uses too. From the mid 70s onwards, digital tape recorders were appearing in studios and vinyl records were being cut from a digital files (DDL).

BBC was not involved with developing CDs with Philips and Sony, least not to my knowledge. CDs made use of digital audio technology which already existed, so they wouldn't need to collab. The innovation was storing the digital data on a laser-read optical disc (laster disc predated CDs but this was analogue) and developing consumer-grade machines to read the CDs, aka CD players.
 

iMark

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Around 1980 the major record companies switched from tape recording to digital recorders for classical recordings. I have quite a few LP's from that era. I remember that the everyone said that the digitally recorded LPs sounded better than the ones recorded with analogue tape recorders: no tape hiss and better signal to noise ratio were the factors everyone seemed to agree on. Another great advantage was that an exact digital copy of a master could be sent to every record pressing plant in the world.

A lot of these early digital recordings were later rereleased on CD. People could hear the difference between LP and CD of the same recording because the CD didn't have any hum, hiss or other noises. I find it very amusing that things have come full circle and audiophiles are now going back to LP playback while knowing full well that a good digital recording (even at CD quality) will always outperform the best analogue recorders. People weren't stupid in the late 1970's when the first digital recorders were built. They were devised to solve a problem: noise of all kinds on analogue tape recordings.
 

andyjm

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Blacksabbath25 said:
Do you think that there are sound differences between CD players and Dacs that some are better managing the jitter better then others so you hear a difference in sound quality because of the jitter management ?
Depending on what study you believe, even gross levels of jitter are undetectable - although it depends on the type of jitter. I think the design of DAC (oversampled / delta sigma etc) and the design of the reconstruction filters are likely to have much more effect.
 

rainsoothe

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iMark said:
Around 1980 the major record companies switched from tape recording to digital recorders for classical recordings. I have quite a few LP's from that era. I remember that the everyone said that the digitally recorded LPs sounded better than the ones recorded with analogue tape recorders: no tape hiss and better signal to noise ratio were the factors everyone seemed to agree on. Another great advantage was that an exact digital copy of a master could be sent to every record pressing plant in the world.

A lot of these early digital recordings were later rereleased on CD. People could hear the difference between LP and CD of the same recording because the CD didn't have any hum, hiss or other noises. I find it very amusing that things have come full circle and audiophiles are now going back to LP playback while knowing full well that a good digital recording (even at CD quality) will always outperform the best analogue recorders. People weren't stupid in the late 1970's when the first digital recorders were built. They were devised to solve a problem: noise of all kinds on analogue tape recordings.

 
What does "outperform" mean, though, in the context of music or hi-fi preferences being subjective? Many vynil enthusiasts acknowledge that digital is more accurate on paper, but they prefer the distortion vynil brings. Also, as I said in another post, live music, more often than not, is distorted as hell, there is no 3d soundstage or instrument separation etc - so one could make the point that digital is too forensic to properly reproduce the feeling of live music. It's a matter of taste, mister Blacksabbath's Yamaha amp is both his better and my worse. Same for digital vs analogue, as ppl listen to music, not watch graphs.
 

Electro

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rainsoothe said:
iMark said:
Around 1980 the major record companies switched from tape recording to digital recorders for classical recordings. I have quite a few LP's from that era. I remember that the everyone said that the digitally recorded LPs sounded better than the ones recorded with analogue tape recorders: no tape hiss and better signal to noise ratio were the factors everyone seemed to agree on. Another great advantage was that an exact digital copy of a master could be sent to every record pressing plant in the world.

A lot of these early digital recordings were later rereleased on CD. People could hear the difference between LP and CD of the same recording because the CD didn't have any hum, hiss or other noises. I find it very amusing that things have come full circle and audiophiles are now going back to LP playback while knowing full well that a good digital recording (even at CD quality) will always outperform the best analogue recorders. People weren't stupid in the late 1970's when the first digital recorders were built. They were devised to solve a problem: noise of all kinds on analogue tape recordings.
What does "outperform" mean, though, in the context of music or hi-fi preferences being subjective? Many vynil enthusiasts acknowledge that digital is more accurate on paper, but they prefer the distortion vynil brings. Also, as I said in another post, live music, more often than not, is distorted as hell, there is no 3d soundstage or instrument separation etc - so one could make the point that digital is too forensic to properly reproduce the feeling of live music. It's a matter of taste, mister Blacksabbath's Yamaha amp is both his better and my worse. Same for digital vs analogue, as ppl listen to music, not watch graphs.
Yes there is . *smile*
 

BigH

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iMark said:
Around 1980 the major record companies switched from tape recording to digital recorders for classical recordings. I have quite a few LP's from that era. I remember that the everyone said that the digitally recorded LPs sounded better than the ones recorded with analogue tape recorders: no tape hiss and better signal to noise ratio were the factors everyone seemed to agree on. Another great advantage was that an exact digital copy of a master could be sent to every record pressing plant in the world.

A lot of these early digital recordings were later rereleased on CD. People could hear the difference between LP and CD of the same recording because the CD didn't have any hum, hiss or other noises. I find it very amusing that things have come full circle and audiophiles are now going back to LP playback while knowing full well that a good digital recording (even at CD quality) will always outperform the best analogue recorders. People weren't stupid in the late 1970's when the first digital recorders were built. They were devised to solve a problem: noise of all kinds on analogue tape recordings.
Most vinyl records now use digital either in the recording or programming/mixing, there is a interesting article by
Noel Summerville about how hard it is to produce an all analogue record, he had to do it once for someone. Many people think when they are buying vinyl they are getting pure analogue. Many recent lps don't even seem to have been remastered from the cd master
 

MajorFubar

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BigH said:
there is a interesting article by Noel Summerville about how hard it is to produce an all analogue record, he had to do it once for someone. Many people think when they are buying vinyl they are getting pure analogue. Many recent lps don't even seem to have been remastered from the cd master
It doesn't even enter their heads that many records for the last 40 years have either been cut from a digital master tape or an analogue master tape fed through a digital delay line (DDL). Digital delay lines were a Godsend because they reduced the number of wasted lacquers and the time taken to cut another. But as consequence it meant the lacquer was cut from a signal which had passed through both an ADC and a DAC on the way to the cutting head.

I wonder how many records cut from either a digital master or through a DDL were purchased by the staunch anti-digital brigade who steadfastly refused to be seen dead with anything digital.
 

nopiano

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Feb 15, 2009
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MajorFubar said:
BigH said:
there is a interesting article by Noel Summerville about how hard it is to produce an all analogue record, he had to do it once for someone. Many people think when they are buying vinyl they are getting pure analogue. Many recent lps don't even seem to have been remastered from the cd master
It doesn't even enter their heads that many records for the last 40 years have either been cut from a digital master tape or an analogue master tape fed through a digital delay line (DDL). Digital delay lines were a Godsend because they reduced the number of wasted lacquers and the time taken to cut another. But as consequence it meant the lacquer was cut from a signal which had passed through both an ADC and a DAC on the way to the cutting head.

I wonder how many records cut from either a digital master or through a DDL were purchased by the staunch anti-digital brigade who steadfastly refused to be seen dead with anything digital.
Indeed, and this is one reason why I’ve kept my LPs from the pre-CD era, a few late ones only being from digital masters. I like the idea of true analogue LP replay from its day, just as DDD CD replay makes sense.

Quite a few great analogue era masters have been salvaged or given new life thanks the popularity of CD for so many years. This applies particularly for ‘classical’ music where restored shellac 78s and other historic material has been brilliantly remastered using modern digital techniques.

Today, it’s harder than ever to know what you’re buying if you buy new records, download or stream. At least in the 1960s and ‘70s it was clear!
 

rainsoothe

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Electro said:
rainsoothe said:
iMark said:
Around 1980 the major record companies switched from tape recording to digital recorders for classical recordings. I have quite a few LP's from that era. I remember that the everyone said that the digitally recorded LPs sounded better than the ones recorded with analogue tape recorders: no tape hiss and better signal to noise ratio were the factors everyone seemed to agree on. Another great advantage was that an exact digital copy of a master could be sent to every record pressing plant in the world.

A lot of these early digital recordings were later rereleased on CD. People could hear the difference between LP and CD of the same recording because the CD didn't have any hum, hiss or other noises. I find it very amusing that things have come full circle and audiophiles are now going back to LP playback while knowing full well that a good digital recording (even at CD quality) will always outperform the best analogue recorders. People weren't stupid in the late 1970's when the first digital recorders were built. They were devised to solve a problem: noise of all kinds on analogue tape recordings.

 
What does "outperform" mean, though, in the context of music or hi-fi preferences being subjective? Many vynil enthusiasts acknowledge that digital is more accurate on paper, but they prefer the distortion vynil brings. Also, as I said in another post, live music, more often than not, is distorted as hell, there is no 3d soundstage or instrument separation etc - so one could make the point that digital is too forensic to properly reproduce the feeling of live music. It's a matter of taste, mister Blacksabbath's Yamaha amp is both his better and my worse. Same for digital vs analogue, as ppl listen to music, not watch graphs.
Yes there is . *smile*
You failed to bold the part where I said "more often than not" :) yes, chamber or orchestral music in an athenaeum, or 4 instrument jazz in a nice cafe might have that, but for instance, at Steven Wilson's concert at Royal Albert Hall, who could point into the direction of the lead guitar with their eyes closed whilst Steven was moving left and right, back and forth? No one. There is no quiet black space around instrument X like I get at home. It was just grander, punchier, gutsier, emotioner :p It didn't sound like an Accuphase amp, as much as I love it's sound and hi-fi capabilities.
 

MajorFubar

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nopiano said:
Today, it’s harder than ever to know what you’re buying if you buy new records, download or stream. At least in the 1960s and ‘70s it was clear!
I'd say it's a dead cert that any LP you buy new today is sourced from a digital file. The only exception might be some specialist release that's making a deliberate song and dance about being cut at the end of an all analogue chain. Though I can't think of one off hand.
 

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