EDIT - I enjoyed the hours of reading and checking to produce this thread, but on posting I think it is wrong to make people read for hours to understand my thoughts. So I have made this summary.....
It is not just about 1s and 0s and some saying they have heard differences despite the 'science'. We need to look at the effects of jitter, which is the timing of the sending of the 1s and 0s, to find a variable which can account for both sides of the argument being correct or wrong, as they have been barking up the wrong tree.
The detail as to why.......
So often digital cable debates are dominated by two camps and descend into circular arguments. One states that it is just 1s and 0s and the other claims they can hear a difference.
I cannot rationalise numerous credible reports from music publications such as What Hifi and forum members who say they can hear a difference, with those equally credible people who say they hear no difference and credible arguments that show there is no difference. So I have been reading and this is what I have come up with.
I am not a scientist. My only experience of different digital cables are the various USB cables I have connected my laptops to DACs with. I cannot say I have noticed any difference. I have done with analogue cables. I do listen analytically, I have good hearing, I can pick out different codecs and bit rates used in music files. I have tester tracks that I am very familiar with to listen for differences. So I am open minded to both side’s arguments.
The main argument that digital cables are the same is that it is just 1s and 0s. For example, you do not have any issues sending a document to a printer down a USB cable. The reason for that is error correction ensures the correct 1s and 0s are sent. If there is an error, data is resent or it breaks up and you would really notice that happening. If the signal does not break up error correction is working fine and the cable has no effect on this. The same applies to both audio and visual digital data transmission. Here I concentrate on audio. I have read nothing that suggests somehow 1s can become 0s or vice versa in a cable. Again error correction stops that. So what are we left with that can be variable?
A word that kept coming up whilst I was reading is jitter. From an online dictionary jitter is “a flicker or fluctuation in a transmission signal or display image. The term is used in several ways, but it always refers to some offset of time and space from the norm. For example, in a network transmission, jitter would be a bit arriving either ahead or behind a standard clock cycle or, more generally, the variable arrival of packets”.
The timing of the data sent is not important to print something. It just needs to be bit perfect and arrive in tact. But timing is very important for music. Furthermore, with music there are very high rates of data being sent that need to be converted to an analogue signal to produce sound in real time, perfectly timed.
To deal with timing the transmission of the data ‘clocks’ are used. The clock is a crystal oscillator where vibration is used to measure time. When data is transmitted a clock signal is also sent. According to Remy Fouree in Stereophile the clock signal is ‘embedded in the pulse edges’. So you could say it is 1s and 0s and a tick that is actually transmitted. Any component involved in digital data transmission has a clock. A DAC has one, including the DAC in your ipod and CD player. For there to be no jitter these clocks have to be incredibly accurate and if more than one is being used at a time, totally in time with each other.
But the clocks themselves can cause jitter, as can any part of the route a digital signal takes from the moment it is recorded and an ADC converts the analogue signal to digital to the point it is converted back to analogue.
So what is the audio effect of jitter? John Swenson from Computer Audio Asylum describes the effect of jitter as a “loss of inner detail”, “a flatter sound” and “improvement in bass articulation”. Cambridge Audio states that jitter is a distortion which is audible as the ear picks out timing errors and needs timing to place information correctly. So jitter “blurs the signal“. Steve Nugent from Empirical Audio describes jitter as looking through old, dirty glass compared to a modern clean pane. Elias Gwinn from Benchmark also attributes jitter to degraded sound quality. A paper by Gannon Kashiwa describes it as ‘noise’ like an added voltage on an analogue signal. Discussions on various forums also attribute jitter to having an over all effect on sound quality as opposed to it having a sound itself.
There is an argument that jitter is not audible below a certain rate, details from Hydrogen audio and numerous linked research papers. But there is no definite agreement what level that is. There are also reports that jitter does not necessarily affect sound quality detrimentally, such as tests by John Swenson. He reports that some audio products which have a higher jitter than others “sound better”. Gannon Kashiwa points to a lack of consistency between the theory and actual experience. Steve Nugent points out that such study is still in its infancy. But there is an acceptance that jitter and timing errors, no matter how small is very likely to be detrimental to audio.
How can or do cables affect jitter? Elias Gwinn describes a cable’s effect on jitter as
“Different cables have different impedances (resistance, capacitance, and inductance), which forms a filter that attenuates high-frequencies. When a digital clock changes states (from a '1' to a '0', for example), it ideally changes instantaneously, but a lack of high-frequency capability causes the transition to be slower.
Also, noise creates inaccuracies during the transition. The most common culprit of noise is signal reflection. Signal reflection is minimized by proper impedance termination and the proper characteristic impedance of the cable. However, poor cable shielding will also allow EMI noise to impurify the signal”
Steve Nugent describes cable effects as not adding to jitter, but cables can slow the signal transitions (the difference between 1s and 0s) which makes it harder for the DAC receiving the data to get the timing correct.
TNT Audio refer to “Line Induced Jitter” where bandwidth limits make transitions slower than ideal and “Interfering-noise induced Jitter” such as the effect of EMI on cables.
Remy Fouree refers to “electrical noise”, “bandwidth limitation“ and “mismatched between transmission and receiver impedance“. He goes on to say that any two cables with the same impedance, no matter the cost will have the same effect on jitter in the same setup. It appears to be your luck as to whether you find the $3 or $300 cable first.
So I do not have a conclusive answer to the digital cable debates. But there is enough evidence to say that the real discussion about digital cables should be about jitter and its effect on data transmission.
In particular with cables it should be how much the cables effects the transmission of data which in turn effects timing and so causes jitter. A perfect cable will have no effect on the jitter contained in the data signal sent and should be a perfect match between sender and receiver.
Here comes the potential irony.
It is debatable that zero jitter is possible, but if you have a very low jitter transport with a very accurate clock sending a low jitter signal to another accurate clock in a very good DAC, the effect of a cable could go either way. It may have no effect as it too causes no jitter. Or it is the cause of a lot of jitter. Different systems will produce different amounts of jitter. Some will possibly even find that jitter may improve the sound for them.
Benchmark are confident enough in their DAC’s ability to deal with jitter that they say it does not matter what transport or cable you use. So, as DACs get better at rejecting jitter, the case for buying a ‘better’ digital cable or claiming different cables have different effects weakens.
That helps to explain why some people hear differences in cables and others do not and as knowledge of jitter and its effects is improved, potentially both sides are correct! Though to prove that we would need a massive test of each persons susceptibility to noticing jitter and how much jitter is present in their system and in particular the cable used.
Sources - I have not linked to any of the sources I have used as they are primarily found through other forums or may be copyrighted (I have not quoted from any source that is clearly marked copyrighted). If you google terms like ‘jitter‘, ‘what does jitter sound like?’ and the names and companies I have referred to you should be able to track them down. The quote from Benchmark’s Elias Gwinn was an answer to a question I put to him on a forum where I have also communicated with Empirical Audio‘s Steve Nugent. I actually have no idea who any of these people really are, but they are referred to a lot in the reading I have done, so I assume they know their stuff enough to satisfy those who want proof and science to the debate.
It is not just about 1s and 0s and some saying they have heard differences despite the 'science'. We need to look at the effects of jitter, which is the timing of the sending of the 1s and 0s, to find a variable which can account for both sides of the argument being correct or wrong, as they have been barking up the wrong tree.
The detail as to why.......
So often digital cable debates are dominated by two camps and descend into circular arguments. One states that it is just 1s and 0s and the other claims they can hear a difference.
I cannot rationalise numerous credible reports from music publications such as What Hifi and forum members who say they can hear a difference, with those equally credible people who say they hear no difference and credible arguments that show there is no difference. So I have been reading and this is what I have come up with.
I am not a scientist. My only experience of different digital cables are the various USB cables I have connected my laptops to DACs with. I cannot say I have noticed any difference. I have done with analogue cables. I do listen analytically, I have good hearing, I can pick out different codecs and bit rates used in music files. I have tester tracks that I am very familiar with to listen for differences. So I am open minded to both side’s arguments.
The main argument that digital cables are the same is that it is just 1s and 0s. For example, you do not have any issues sending a document to a printer down a USB cable. The reason for that is error correction ensures the correct 1s and 0s are sent. If there is an error, data is resent or it breaks up and you would really notice that happening. If the signal does not break up error correction is working fine and the cable has no effect on this. The same applies to both audio and visual digital data transmission. Here I concentrate on audio. I have read nothing that suggests somehow 1s can become 0s or vice versa in a cable. Again error correction stops that. So what are we left with that can be variable?
A word that kept coming up whilst I was reading is jitter. From an online dictionary jitter is “a flicker or fluctuation in a transmission signal or display image. The term is used in several ways, but it always refers to some offset of time and space from the norm. For example, in a network transmission, jitter would be a bit arriving either ahead or behind a standard clock cycle or, more generally, the variable arrival of packets”.
The timing of the data sent is not important to print something. It just needs to be bit perfect and arrive in tact. But timing is very important for music. Furthermore, with music there are very high rates of data being sent that need to be converted to an analogue signal to produce sound in real time, perfectly timed.
To deal with timing the transmission of the data ‘clocks’ are used. The clock is a crystal oscillator where vibration is used to measure time. When data is transmitted a clock signal is also sent. According to Remy Fouree in Stereophile the clock signal is ‘embedded in the pulse edges’. So you could say it is 1s and 0s and a tick that is actually transmitted. Any component involved in digital data transmission has a clock. A DAC has one, including the DAC in your ipod and CD player. For there to be no jitter these clocks have to be incredibly accurate and if more than one is being used at a time, totally in time with each other.
But the clocks themselves can cause jitter, as can any part of the route a digital signal takes from the moment it is recorded and an ADC converts the analogue signal to digital to the point it is converted back to analogue.
So what is the audio effect of jitter? John Swenson from Computer Audio Asylum describes the effect of jitter as a “loss of inner detail”, “a flatter sound” and “improvement in bass articulation”. Cambridge Audio states that jitter is a distortion which is audible as the ear picks out timing errors and needs timing to place information correctly. So jitter “blurs the signal“. Steve Nugent from Empirical Audio describes jitter as looking through old, dirty glass compared to a modern clean pane. Elias Gwinn from Benchmark also attributes jitter to degraded sound quality. A paper by Gannon Kashiwa describes it as ‘noise’ like an added voltage on an analogue signal. Discussions on various forums also attribute jitter to having an over all effect on sound quality as opposed to it having a sound itself.
There is an argument that jitter is not audible below a certain rate, details from Hydrogen audio and numerous linked research papers. But there is no definite agreement what level that is. There are also reports that jitter does not necessarily affect sound quality detrimentally, such as tests by John Swenson. He reports that some audio products which have a higher jitter than others “sound better”. Gannon Kashiwa points to a lack of consistency between the theory and actual experience. Steve Nugent points out that such study is still in its infancy. But there is an acceptance that jitter and timing errors, no matter how small is very likely to be detrimental to audio.
How can or do cables affect jitter? Elias Gwinn describes a cable’s effect on jitter as
“Different cables have different impedances (resistance, capacitance, and inductance), which forms a filter that attenuates high-frequencies. When a digital clock changes states (from a '1' to a '0', for example), it ideally changes instantaneously, but a lack of high-frequency capability causes the transition to be slower.
Also, noise creates inaccuracies during the transition. The most common culprit of noise is signal reflection. Signal reflection is minimized by proper impedance termination and the proper characteristic impedance of the cable. However, poor cable shielding will also allow EMI noise to impurify the signal”
Steve Nugent describes cable effects as not adding to jitter, but cables can slow the signal transitions (the difference between 1s and 0s) which makes it harder for the DAC receiving the data to get the timing correct.
TNT Audio refer to “Line Induced Jitter” where bandwidth limits make transitions slower than ideal and “Interfering-noise induced Jitter” such as the effect of EMI on cables.
Remy Fouree refers to “electrical noise”, “bandwidth limitation“ and “mismatched between transmission and receiver impedance“. He goes on to say that any two cables with the same impedance, no matter the cost will have the same effect on jitter in the same setup. It appears to be your luck as to whether you find the $3 or $300 cable first.
So I do not have a conclusive answer to the digital cable debates. But there is enough evidence to say that the real discussion about digital cables should be about jitter and its effect on data transmission.
In particular with cables it should be how much the cables effects the transmission of data which in turn effects timing and so causes jitter. A perfect cable will have no effect on the jitter contained in the data signal sent and should be a perfect match between sender and receiver.
Here comes the potential irony.
It is debatable that zero jitter is possible, but if you have a very low jitter transport with a very accurate clock sending a low jitter signal to another accurate clock in a very good DAC, the effect of a cable could go either way. It may have no effect as it too causes no jitter. Or it is the cause of a lot of jitter. Different systems will produce different amounts of jitter. Some will possibly even find that jitter may improve the sound for them.
Benchmark are confident enough in their DAC’s ability to deal with jitter that they say it does not matter what transport or cable you use. So, as DACs get better at rejecting jitter, the case for buying a ‘better’ digital cable or claiming different cables have different effects weakens.
That helps to explain why some people hear differences in cables and others do not and as knowledge of jitter and its effects is improved, potentially both sides are correct! Though to prove that we would need a massive test of each persons susceptibility to noticing jitter and how much jitter is present in their system and in particular the cable used.
Sources - I have not linked to any of the sources I have used as they are primarily found through other forums or may be copyrighted (I have not quoted from any source that is clearly marked copyrighted). If you google terms like ‘jitter‘, ‘what does jitter sound like?’ and the names and companies I have referred to you should be able to track them down. The quote from Benchmark’s Elias Gwinn was an answer to a question I put to him on a forum where I have also communicated with Empirical Audio‘s Steve Nugent. I actually have no idea who any of these people really are, but they are referred to a lot in the reading I have done, so I assume they know their stuff enough to satisfy those who want proof and science to the debate.
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