Amplitude and Time, how difficult can it be ?

Rob Sonata · Mar 5, 2017

A good friend of mine (famed musician, producer and audio engineer) had a favourite phrase - 'Sound is music and music is sound'

I suppose his reasoning was that both are inseparable and that without the medium of 'sound' we could not have the creative art form that is 'music' ?

Another abiding statement that has stayed with me from my student days, given to me by a well known Professor, was to always begin solving a problem by going back to 'first principles' or 'fundamentals' and take it from there.....

It seems quite obvious to me, from reading the posts and questions outlined on this forum, that the reproduction of recorded audio is a big problem for a lot of people here - am I correct in thinking that ?

So, I keep asking myself why and I keep coming to the same conclusion:

Sound is simple, it's just Amplitude and Time (the 'first principles' thing) and yet every audio manufacturer (with the exception of one) seems to ignore the aspect of Time distortion in their products.

Why ?

Recent studies and medical advances are now showing us, that more than ever, we are incredibly sensitive to information in the time domain - particularly in our hearing mechanism and psycho-acoustic processing.

Therefore, all I can conclude is that 'audiophiles' (as separate from musicians, music lovers, etc) are content to live with this lack of time coherence in their systems even though it is something that does not exist in 'real' sound..... listening to the world through 'rose tinted' receptacles.

Finally, just to clarify my point, in our natural world when a sound is produced, all of the frequencies present within that complex pressure wave reach our ear at the same time (there is no group delay between the low and high frequencies) and that's why we can tell instantly that this sound is real.
However, in all audio reproduction systems that I have heard (with the exception of one), there is an unnatural distortion of this time relationship (by filters, amplifier circuits, cables, crossovers, speaker cabinets....) and I can hear it instantly as being an 'unreal' sound, or just another 'hifi' system.

What I can't understand fully, is why are audio manufacturers and audiophiles only concerned with the Amplitude component of sound and not the Time aspect, when it seems to me that the time issue is the most important.

Is it because the Time component is more difficult to recreate and more expensive to do correctly ?

Please let me know your thoughts, people.

RogerD · Mar 5, 2017

Look before you leap,the water is very deep.

Ken Newton · Mar 5, 2017

Unfortunately, your thesis seems mostly assertion and supposition. How did you come by the conclusion that only one vendor is concerned with time domain performance? I'd wager that the large majority of vendors, if not all of them, believe that transient response can be musically significant. Certainly, they don't ignore it. System and device bandwidth limitations being a practical reality, total system optimization for time domain performance will trade-off degraded frequency domain performance.

Rob Sonata · Mar 5, 2017

RogerD said:
Look before you leap,the water is very deep.

Yes, I'm sure it's deeper than Loch Ness out there and I don't want to anger any mythical monsters but it just seems that every discussion revolves around the 'amplitude' component (maybe because it's easier to hear and write about) and the time component (or the relative time distortion of frequencies across the audible spectrum) is largely ignored - surely we want to hear everything at the right time, just as we do in our natural environment ?

Rob Sonata · Mar 5, 2017

Ken Newton said:
Unfortunately, your thesis seems mostly assertion and supposition. How did you come by the conclusion that only one vendor is concerned with time domain performance? I'd wager that the large majority of vendors, if not all of them, believe that transient response can be musically significant. Certainly, they don't ignore it. System and device bandwidth limitations being a practical reality, total system optimization for time domain performance will trade-off degraded frequency domain performance.

Apologies Ken, I did not intend to assert or suppose anything.

I only wondered why the very important aspect of maintaining the correct time relationship between the frequencies across the audible bandwidth seems to be considered irrelevant in hifi.

As you have pointed out to me, it maybe due to the fact that this is requires a system wide approach to ensure that the time coherence can be maintained from the start point to the end point.

Having said that, when you hear a system that is able to do that, it's very impressive.

morricab · Mar 5, 2017

Ken Newton said:
Unfortunately, your thesis seems mostly assertion and supposition. How did you come by the conclusion that only one vendor is concerned with time domain performance? I'd wager that the large majority of vendors, if not all of them, believe that transient response can be musically significant. Certainly, they don't ignore it. System and device bandwidth limitations being a practical reality, total system optimization for time domain performance will trade-off degraded frequency domain performance.

Well given that most loudspeakers don't preserve phase and therefore time information I would not agree that most care with time coherence.

amirm · Mar 5, 2017

Rob Sonata said:
Apologies Ken, I did not intend to assert or suppose anything.

I only wondered why the very important aspect of maintaining the correct time relationship between the frequencies across the audible bandwidth seems to be considered irrelevant in hifi.

I think it will be a struggle to find marketing material for anything high-end that doesn't dabble or claim timing accuracy as such. Whether they get there or not is a different matter.

Back to your post, you say that we, our hearing, has such abilities. Best lay method to know whether such a thing should exist in our perception, is to go back and look at evolutionary threats to our existence. Take the early human walking in the brush and hearing a sound. Differential timing between the sound arriving at each ear would let us locate the direction and even height of the sound. And that ability allowed us to have higher chance of staying alive should that noise be the sound of a lion coming to eat us!

It is for the above reason that even small timing differences between two audio channels causes the stereo image to shift. Ironically mass market products with built-in DSP and room equalization deal with this far more perfectly than any high-end audio system by measuring the arriving time of sound from each speaker and inserting delays to get them to match. No tape measure needed!

Now, why do you think from evolutionary point of view the human perception should have cared about arrival time of all the frequencies being the same? And do you think such a hypothesis has or has not been tested?

RogerD · Mar 5, 2017

Rob Sonata said:
Yes, I'm sure it's deeper than Loch Ness out there and I don't want to anger any mythical monsters but it just seems that every discussion revolves around the 'amplitude' component (maybe because it's easier to hear and write about) and the time component (or the relative time distortion of frequencies across the audible spectrum) is largely ignored - surely we want to hear everything at the right time, just as we do in our natural environment ?

Rob, How many speakers can throw a very coherent and transparent soundfield? In this day of computer modeling you would think many should be able to. There are many factors that can effect the outcome,speaker placement,system wide noise and distortion,to name a few. As you mention time domain implementation can be very impressive when it is displayed. I know this from experience.

Rob Sonata · Mar 5, 2017

morricab said:
Well given that most loudspeakers don't preserve phase and therefore time information I would not agree that most care with time coherence.

Thank you, Morricab.

This is precisely my point, nearly every loudspeaker ever made creates this time distortion (due to passive crossovers) but nobody seems to care and just brushes this massive problem under the carpet, why ?

We also see some cable manufacturers willingly putting filters into their products (thus messing with 'time') and manufacturers of amplifiers who limit their bandwidths using filters that cause group delays across the audible spectrum too.... and then we have anti-aliasing filters used in digital products,.... and output transformers, input transformers...... the list goes on...

Time is precious, don't mess with it

Rob Sonata · Mar 5, 2017

RogerD said:
Rob, How many speakers can throw a very coherent and transparent soundfield? In this day of computer modeling you would think many should be able to. There are many factors that can effect the outcome,speaker placement,system wide noise and distortion,to name a few. As you mention time domain implementation can be very impressive when it is displayed. I know this from experience.

Hi Roger, I have heard a number of systems that purport to be perfectly aligned in the time domain (but they are then let down by other aspects within their system - cables, amplifiers and speaker cabinet resonance) - at least they are trying to move in the right direction.

Also, some enlightened speaker manufacturers are seeking out collaborations with other companies to help develop time coherent digital crossovers, etc

However, I know of only one manufacturer that takes the whole time-coherence thing right across their entire system (DSP, DACs, Amplifiers, Signal transfer and Speaker enclosure resonance) and they've been pursuing this goal for 40 years.

Even they admit that there is still a huge amount of work to be done to improve things further (active acoustic correction being one area) but the resulting sound so far, is the most 'realistic' that I have heard.

Exciting times ahead !

Rob Sonata · Mar 5, 2017

amirm said:
I think it will be a struggle to find marketing material for anything high-end that doesn't dabble or claim timing accuracy as such. Whether they get there or not is a different matter.

Back to your post, you say that we, our hearing, has such abilities. Best lay method to know whether such a thing should exist in our perception, is to go back and look at evolutionary threats to our existence. Take the early human walking in the brush and hearing a sound. Differential timing between the sound arriving at each ear would let us locate the direction and even height of the sound. And that ability allowed us to have higher chance of staying alive should that noise be the sound of a lion coming to eat us!

It is for the above reason that even small timing differences between two audio channels causes the stereo image to shift. Ironically mass market products with built-in DSP and room equalization deal with this far more perfectly than any high-end audio system by measuring the arriving time of sound from each speaker and inserting delays to get them to match. No tape measure needed!

Now, why do you think from evolutionary point of view the human perception should have cared about arrival time of all the frequencies being the same? And do you think such a hypothesis has or has not been tested?

Hi Amir, unfortunately I think the answer to your question is way beyond my 'pay grade'

I think we, as humans have evolved to survive in our natural environment and it's an environment devoid of time distortion (none of us has the ability to alter time - Dr Who does not exist

Therefore, we instinctively know when a sound we hear is real - be it my wife snapping her fingers, the cat meowing or our neighbour knocking on the front door and yet, when we hear a sound reproduced on a hifi system, we instantly know it's not real (due to time distortion)

Anyone can tell instantly and instinctively when the sound of an acoustic guitar in the next room is real or reproduced by a hifi.... and that's nothing to do with the amplitude (loudness) of the sound but everything to do with the time.

RogerD · Mar 5, 2017

Rob Sonata said:
Hi Roger, I have heard a number of systems that purport to be perfectly aligned in the time domain (but they are then let down by other aspects within their system - cables, amplifiers and speaker cabinet resonance) - at least they are trying to move in the right direction.

Also, some enlightened speaker manufacturers are seeking out collaborations with other companies to help develop time coherent digital crossovers, etc

However, I know of only one manufacturer that takes the whole time-coherence thing right across their entire system (DSP, DACs, Amplifiers, Signal transfer and Speaker enclosure resonance) and they've been pursuing this goal for 40 years.

Even they admit that there is still a huge amount of work to be done to improve things further (active acoustic correction being one area) but the resulting sound so far, is the most 'realistic' that I have heard.

Exciting times ahead !

Rob, the manufacturer that developed my speakers,psycho acoustics circuit,and amplifiers used time domain analysis during the 1980's up to the early 1990's. The sound has always impressed me,of course that's why I made the purchase.

Speedskater · Mar 5, 2017

Almost every home theater receiver has channel time controls. With sound moving through air, time has to be a consideration. I hope that the microsecond dead horse doesn't come to life again.

PeterA · Mar 5, 2017

Rob Sonata said:
So, I keep asking myself why and I keep coming to the same conclusion:

Sound is simple, it's just Amplitude and Time (the 'first principles' thing) and yet every audio manufacturer (with the exception of one) seems to ignore the aspect of Time distortion in their products.

Rob, are your referring to Wilson Audio's new WAMM model?

Ken Newton · Mar 5, 2017

morricab said:
Well given that most loudspeakers don't preserve phase and therefore time information I would not agree that most care with time coherence.

It depends on whether the phase shift is linear or non-linear, as to whether time information is preserved. A linear phase shift does not distort time, it produces a constant flat time delay. The bigger issue, I think, is that accurately preserving phase and transient information is exceedingly difficult for certain equipment (especially for transducers), and usually then entails accepting other important performance trade-offs. Such as, bandwidth, frequency response flatness and dynamic range (which is especially problematic for loudspeaker drivers). In addition, many studies cast doubt on the audibility of phase, while transient reposnse is accepted as audible. Phase response and transient response are not synonymous.

As for many things, the proof of the pudding is in the tasting. The proof of the subjective performance of total time coherence is in the listening. Some hear what they believe is the benefit of time optimization, while others either do not hear or do not accept the trade-offs they hear in order to have time optimization.

Whatmore · Mar 5, 2017

PeterA said:
Rob, are your referring to Wilson Audio's new WAMM model?

Sanders speakers are time aligned, as too are a couple of Aussie manufacturers- SGR, Kyron, Legend.

I'm sure there are more. Surprised at the claim that only one company does it

Fiddle Faddle · Mar 5, 2017

Rob Sonata said:
Sound is simple, it's just Amplitude and Time (the 'first principles' thing) and yet every audio manufacturer (with the exception of one) seems to ignore the aspect of Time distortion in their products.

I am really baffled as to how you came to that conclusion. It is one of the most discussed attributes of good componentry and good reproduction. If you read professional reviews of products it is also much discussed. And just to contradict your statement with one example:

http://www.analogplanet.com/content...udspeaker-reaches-heavens#Gx7iIGF9B3HUlPHC.97

And I may or may not be the exception here, but I rate time domain performance extremely highly - in that for me it is absolutely critical to the quality of a component - almost above all else except the most obvious things.

Folsom · Mar 5, 2017

I don't believe this thread has any value.

All manufacturers are doing their best to account for everything. Just because they haven't marketed it to you doesn't mean you've found the missing-link.

No laymen is going to walk in and solve everything. But I suppose all these pet theories do keep people busy.

Don Hills · Mar 6, 2017

Rob Sonata said:
Hi Amir, unfortunately I think the answer to your question is way beyond my 'pay grade' ...
... Anyone can tell instantly and instinctively when the sound of an acoustic guitar in the next room is real or reproduced by a hifi.... and that's nothing to do with the amplitude (loudness) of the sound but everything to do with the time.

That's a conclusion that's above your pay grade. What leads you to believe that timing is the answer? Sure, it could be, but how did you get there?

Rob Sonata · Mar 6, 2017

Speedskater said:
Almost every home theater receiver has channel time controls. With sound moving through air, time has to be a consideration. I hope that the microsecond dead horse doesn't come to life again.

Hi, yes you will definitely need some control over the delay times in an A/V system (akin to those that I used for large PA installations in my 'live' sound days) as this is used to ensure that the placement proximity of the various speaker channels combine to produce a sound that is 'in-sync' at the listening position.

What I am asking about is a bit more subtle than that, this involves the time distortion of various frequencies within each audio signal and that fact that higher frequencies are unnaturally displaced from their correct point in time by components such as amplifiers, transformers, passive crossovers and filtered cables.

This effect would still occur in an AV system that may well be synchronised for placement delays but not for the time distortions that are present within each of those individual system signal paths (the various amplifier channels, passive crossovers in each speaker, and so on)

Amplitude and Time, how difficult can it be ?

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