[x RELIC x]

The million dollar question in a headphone forum... What's Rob's favourite headphone?

 

[SearchOfSub]

Hello Rob, just wondering if you think each and every dac that is the same model that are mass produced have equal and identical sound quality? - in particular with dacs that you manufacture. In the past I've had the exact same dac that have been mass produced and although exact same model, they sounded different all three times.(not Chord but diff. company) The difference was there with the same model made from the same company for me to label it an average dac into an audiophille dac. The 2-5 percent improvement was there between the 3 same dacs which surprised me. I am not sure if the issue was with burn-in but clearly there was enough difference in air and extension between the 3 of the same model and I am sure it wasn't placebo either.

 

[mmerrill99]

Great post on listening, Rob - wise words

Totally agree with you that what happens in auditory processing is the fascinating part of all of this & where a large part of the friction exists between the measurement fanatics & the people who actually listen.
It's interesting that we have frequency filter banks (ERBs), amplitude modulation filter banks & it also appears that we store & use summary statistical analysis of sounds. Just the processing involved in these three elements alone (& there are more) can result in a very different auditory perception than the measurements of amplitude, frequency & time would suggest. By finding out more about auditory perception, we can hopefully design more appropriate measurements or at the very least realise where the limitations of our measurements lie.

I'm interested in the three or four aspects you mention: low level signal linearity, timing accuracy, phase linearity & noise floor modulation.

Maybe in a future installment you can talk a bit bout these & where you have encountered the limitations of existing measurements in characterising these elements?

 

[Stillhart]

Great post that has given me much food for thought.  Thanks for taking the time!
 
Something I'd like to see in further posts is perhaps examples of songs (or parts of songs, more likely) that demonstrate well some of the listening criteria you spoke of.  We all have the glossary to understand the words, but some of us may not have the experience to link the words to the sounds.

 

[tonykaz]

Hello Mr. Watts,
 
Nice to see you answering Mails. 
 
I have to say I'm impressed by your shinny headed buddy that travels around showing off your designs, I didn't expect to hear from you ( much ), rather I'd thought they kept you kinda locked-up in that English Prison look'n Building. 
 
I suppose you realize that there's scads of Mojo action here on Head-fi, I think that Bird named guy in Japan says the Mojo is "his" product of the Year ( which year, I don't know, yet ).  I'm watching the Mojo because of all those little add-on bits you lads are say'n your gonna release and because I have a soft-spot for Brit Stuff & system approach ( I'm a big fan of the Meridian Active Speakers since the mid 1980s & the now obsolete Linn LP12 ).
 
I suspect that I don't quite know what any of my music actually sounds like.  I do enjoy [size=x-small]my Schiit Asgard 2 Amp and Sennheiser HD series headphones, I [/size]doubt they are accurate enough for a Mastering Engineer.  I'm even considering a Tube Amp so that I can go crazy "rolling" Russian and French Tubes but I've held off, for some reason.
 
The word I hear ( about your stuff ) is your DAC is the "hot" item!, it can make recordings even more listenable, which ( I'm told ) DACs are not supposed to be able to do. 
 
So, I'm sort-of planning on owning some Chord stuff :  the little Mojo and some little add-on items you announced but haven't released yet.  
 
I initially held off looking at the Mojo because it "only" has 38 Miliwatts output and I though my Senneiser HD headphones required 200 Miliwatts!, silly me, turns out they only need .2 milliwatts to reach 90db.  ( why do I need an Amp that features 2 Watts output? ) 
 
I'm hoping that you lads hang in there for a good long time and even get one of those fancy Awards from the Queen ( like Raymound Cooke did ) , maybe even a "K"! 
I'd buy even more stuff from y'all if you were Sir.Robert Watts.  
 
Wish you well,
 
Tony in Michigan 
 
ps.  I'd love to hear about Class "D" Amplification!   I've kinda been a fan of Class "A" headphone Amps but  very much loved my Electrocompaniet Class AB stuff.  Now, Genelec is using Class D to good result. So, I probably should get-on with a full range of 21st Century design technology.  I've been "Old-School" long enough, haven't I ? 
 
ps. no 2.   Lots of Aussies are following y'all, does anyone know why they "talk" with a strange accent?  

 

[Rob Watts]

The million dollar question in a headphone forum... What's Rob's favourite headphone?

Speaking personally - my current favourite is the AQ Nighthawks.
 
Now they are not to every ones taste - a lot of guys at Chord find them way too dark and smooth - but I like them because I can play for 12 hours and am still hungry for more music. By comparison, to me, other HP sound distorted. Moreover, they sound like loudspeakers in terms of tonal balance, and I mostly listen to loudspeakers.
 
Do they have faults - yes, they could be more transparent, and the bass is maybe softer than I would like - but they do so many things right.
 
I have been very impressed with Mr. Speakers Ether too - and have a pair of Ether C (HP is mostly in aircraft for me) coming.
 
Rob

 

[Rob Watts]

Hello Rob, just wondering if you think each and every dac that is the same model that are mass produced have equal and identical sound quality? - in particular with dacs that you manufacture. In the past I've had the exact same dac that have been mass produced and although exact same model, they sounded different all three times.(not Chord but diff. company) The difference was there with the same model made from the same company for me to label it an average dac into an audiophille dac. The 2-5 percent improvement was there between the 3 same dacs which surprised me. I am not sure if the issue was with burn-in but clearly there was enough difference in air and extension between the 3 of the same model and I am sure it wasn't placebo either.

My practical experience of other DAC's is very limited. But that said, I used to have massive problems with consistency maybe 25 years ago - each DAC measured differently, sounded different, and had big break-in periods. This was not good, so I had to go through many many design iterations and changes to make each DAC measure and sound the same, with minimal break-in period. I can't talk about what needed to change, as it would take too long, but it was this variability that set me down the path of designing Pulse Array DAC's. 
 
Today, I don't have this problem - for example, Mojo is made in the tens of thousands - and every one would have the same DR measurements to a fraction of a dB - and they all sound virtually the same.
 
Inconsistency, and break-in are good design problems to have - because it gives you opportunities to improve. By this I mean if there is a SQ change with break-in, then you have a distortion or error mechanism that is not being minimized correctly - so you then have to find out what it is, then reduce that error - then you end up with much bigger steps forward than simply letting devices burn in. I will give you an example - electrolytics take 3 months for the impedance and leakage current to fall. If you have a circuit that is sensitive to this, then it will take 3 months for SQ to improve. But if you redesign the circuit so that the impedance is not important by eliminating the error in the first place - then you will get an even bigger improvement - plus no break-in.
 
Today, brain break-in is by far the biggest variable.
 
Rob

 

[x RELIC x]

Speaking personally - my current favourite is the AQ Nighthawks.

Now they are not to every ones taste - a lot of guys at Chord find them way too dark and smooth - but I like them because I can play for 12 hours and am still hungry for more music. By comparison, to me, other HP sound distorted. Moreover, they sound like loudspeakers in terms of tonal balance, and I mostly listen to loudspeakers.

Do they have faults - yes, they could be more transparent, and the bass is maybe softer than I would like - but they do so many things right.

I have been very impressed with Mr. Speakers Ether too - and have a pair of Ether C (HP is mostly in aircraft for me) coming.

Rob

Very interested to read that you like the Nighthawks. Please update your impressions on the ETHER C when you get them. I own a pair and I'm quite happy with them, but they are certainly not a dark headphone. Interested in your thoughts on them. Thanks Rob.

 

[ddaktiv]

Hi Mr. Watts, we've met briefly at the audio show at Singapore. I love the mojo! but it gets really hot and I know it's supposed to get hot but does it automatically shut down?
I was using it for about 2.5 hours in an airconditioned office (zx2 lined out to mojo and mojo lined out to my amp..) Checked the battery and it's displaying green so tried it again but it did the same thing 2 mins later. When I touched it it was extremely hot. Wondering if it's a faulty unit?

 

[kkcc]

I'm sure Rob will be kind enough to answer any mojo Hugo or dave questions but I would suggest it might be best if we can keep product specific discussion to their respective threads, and keep this on a more general discussion focused on Rob's blog entries.

We all know how fast the Hugo/Mojo threads go with the daily bombardment of product questions and not sure if we want to turn this into another helpdesk....

Cheers

 

[avitron142]

 
Difficulties in listening  
 
Placebo - convince yourself that your system sounds a lot better - and invariably it will. So your frame of mind is very important, so it's essential that when doing listening tests you are a neutral observer, with no expectations. This is not as easy as it sounds, but practice and forcing your mental and emotional state to be neutral helps.

 
Wouldn't looking over measurements invariably convince you that the product "sounds like the measurements", however you interpret the measurements to be? For example, you mentioned small signal non-linearity causes a number of issues in the listening tests. If someone else believed that a different factor causes these issues, and he sees this different "problem", won't he be convincing himself during the listening tests that the SQ has these issues, while he may be totally off in interpreting the measurements?
 
Because of this, I think the best way to do listening tests is before the measurements (for those good people that have the equipment to do them), so your ear doesn't know what to "expect".
 
I also met a few reviewers that don't believe in differences in soundstage. As a AKG K7xx/702 fan, soundstage is my bread and butter, and from listening tests, I thought some DAC's soundstage were larger than others, or, more accurately, some were smaller than what I would expect.
 
As I'm painfully ignorant when it comes to measurements (I'm only 20, I haven't had time to become an engineer yet), are there measurements that an accurately gauge soundstage? Or is it something that can only be told by ear alone? I know a few people who believe the differences aren't there, possibly because they don't see any difference in measurements... which isn't something I'm too comfortable with. After all, musicality (which they might not believe in either) also doesn't seem to have a reliable measurement.
 
But instead of me guessing and speculating, which of the listening test point can be seen in graphs, and which should be left up to the ear? I'm especially interested in soundstage, but it's an important question regarding all of the listening points. 

 

[ddaktiv]

I'm sure Rob will be kind enough to answer any mojo Hugo or dave questions but I would suggest it might be best if we can keep product specific discussion to their respective threads, and keep this on a more general discussion focused on Rob's blog entries.

We all know how fast the Hugo/Mojo threads go with the daily bombardment of product questions and not sure if we want to turn this into another helpdesk....

Cheers

Apologies. Will post on the other thread. Mojo is the first Chord product I've owned and it's supremely awesome and I love it to bits

 

[Rob Watts]

   
Wouldn't looking over measurements invariably convince you that the product "sounds like the measurements", however you interpret the measurements to be? For example, you mentioned small signal non-linearity causes a number of issues in the listening tests. If someone else believed that a different factor causes these issues, and he sees this different "problem", won't he be convincing himself during the listening tests that the SQ has these issues, while he may be totally off in interpreting the measurements?
 
Because of this, I think the best way to do listening tests is before the measurements (for those good people that have the equipment to do them), so your ear doesn't know what to "expect".
 
I also met a few reviewers that don't believe in differences in soundstage. As a AKG K7xx/702 fan, soundstage is my bread and butter, and from listening tests, I thought some DAC's soundstage were larger than others, or, more accurately, some were smaller than what I would expect.
 
As I'm painfully ignorant when it comes to measurements (I'm only 20, I haven't had time to become an engineer yet), are there measurements that an accurately gauge soundstage? Or is it something that can only be told by ear alone? I know a few people who believe the differences aren't there, possibly because they don't see any difference in measurements... which isn't something I'm too comfortable with. After all, musicality (which they might not believe in either) also doesn't seem to have a reliable measurement.
 
But instead of me guessing and speculating, which of the listening test point can be seen in graphs, and which should be left up to the ear? I'm especially interested in soundstage, but it's an important question regarding all of the listening points. 

There is always a danger of expectation bias affecting listening tests - that's why you have to be a completely neutral observer and condition your mind and emotions before hand. But actually the problems with listening tests are not quantitative but qualitative - you can easily hear a difference, and its possible to (fairly) accurately describe the difference - but its actually determining whether the change represents an improvement or not. For example - let's say the sound is brighter - that naturally means that details are easier to hear - now is this brightness down to improved transparency, which normally sounds brighter, and gives better detail resolution - or is it down to increased noise floor modulation, which actually sounds very similar, particularly when you are making tiny changes? Sometimes, its almost impossible to decide using AB testing - the only way of knowing is by checking for the musicality, and that takes a long time.
 
I guess the issue I was talking about was in situations where there are large measurable problems, because that would resolve the issue - if you measure more noise floor modulation, then you know for certain. The problem we have today is that we can hear changes when there are no measurable changes, then the only way of making the right qualitative decision is by knowing before hand what you are doing technically.
 
My post ran out of time, as I actually wanted to add a section about my design goals, and how I use listening tests in practice. That's the plan for my next blog post.
 
Going back to sound stage - no there are no measurements for sound stage directly (excepting gross errors). Now I associate depth with small signal non-linearity - but my DAC's have had perfect small signal linearity for many years. Indeed, before Dave, I thought there was no more improvements to be had with depth, in that the losses we hear with reproduced sound is down to the ADC and mastering. That was not an unreasonable assumption, as Hugo noise shapers already had 1000 times more small signal accuracy than conventional noise shapers, and zero measurable fundamental linearity (to do this I had long ago given up on traditional measurements - I use a -120dB signal and measure how accurate it is at -120dB using an FFT).
 
But the thing about assumptions is one needs to test them with listening tests - and with Dave I had loads of FPGA space, so could have better noise shapers - and increasing the performance of the noise shaper did improve depth. But it changed no other aspect of sound quality. In the end, I had noise shapers that were a trillion times better than conventional, and at each improvement in noise shaper performance it largely (sometimes it didn't but that's way too complex to talk about) had deeper depth.
 
But although we are limited with measurements, with digital design work you can run Verilog simulations which will give you bit perfect data on the performance of your digital circuit - so you can look at very small errors, then listen to them via the FPGA. So we can actually quantify (measure) very small errors, then see if they have any audible consequences. If you can put a number on an effect, then it means you really understand the phenomena, and modern tools allows this kind of analysis.
 
Rob

 

[mmerrill99]

Wouldn't looking over measurements invariably convince you that the product "sounds like the measurements", however you interpret the measurements to be? For example, you mentioned small signal non-linearity causes a number of issues in the listening tests. If someone else believed that a different factor causes these issues, and he sees this different "problem", won't he be convincing himself during the listening tests that the SQ has these issues, while he may be totally off in interpreting the measurements?

Because of this, I think the best way to do listening tests is before the measurements (for those good people that have the equipment to do them), so your ear doesn't know what to "expect".

That's a great question & one that many objectivists/measurists should take note of (Rob is not one of these - I'm talking about the usual armchair engineers) - the "belief" that measurements tell all there is to be heard is a very strong negative biasing factor (nocebo) & one bias that is not changed by blind testing - hearing no difference is the default result from ABX testing.

You are correct - to avoid this scenario, blind listening tests should be done before measurements

 

[mmerrill99]

Rob, can I ask your thoughts on the distortions in digital audio itself - I think you touched on it before when you mentioned the idea of brain burn-in i.e. that the brain has to accommodate to the new types of distortions that have been introduced as a result of digital audio?

It seems to me that the introduction of digital audio have allowed new distortions to be created due to the fact that mathematical processing can be inaccurate in so many new ways that introduce new distortions which were never encountered before in the natural world of vibrating bodies