MQA creator Bob Stuart answers questions.

[Sergei]

What?

What has the missing fundamental effect got to do with this? A speaker that cannot reproduce the fundamental, but can produce the harmonics, can result in the brain interpreting the sound as including the fundamental. That is nothing to do with any so called "biological low pass filter".

Funny, I seem to be seeing connections where others don't. Strength or weakness? Maybe both.

Here's how I approach it: there is (very likely) a high-frequency PWM signal going to the piezo; there is a subjective sensation of low frequency sound => there got to be a mechanism effectively doing the job of LPF somewhere in between.

Whether it is through the missing fundamental effect, or through detecting fundamental frequency of the envelope of the higher-frequency amplitude-modulated carrier, or through some other mechanism, I don't know - I haven't heard this particular toy.

However, there doesn't appear to be an electronic or mechanical LPF in that part of the delivery chain, so the mechanism that does the job of LPF got to be biological. This dispute starts reminding me

 

[Cosmik]

Funny, I seem to be seeing connections where others don't. Strength or weakness? Maybe both.

Here's how I approach it: there is (very likely) a high-frequency PWM signal going to the piezo; there is a subjective sensation of low frequency sound => there got to be a mechanism effectively doing the job of LPF somewhere in between.

Whether it is through the missing fundamental effect, or through detecting fundamental frequency of the envelope of the higher-frequency amplitude-modulated carrier, or through some other mechanism, I don't know - I haven't heard this particular toy.

However, there doesn't appear to be an electronic or mechanical LPF in that part of the delivery chain, so the mechanism that does the job of LPF got to be biological. This dispute starts reminding me

Doesn't "low pass filter" imply that there is something for it to pass? Isn't the idea of the missing fundamental effect that the brain 'hears' something that was never there in the first place? It isn't filtering something, but is synthesising a perception of something.

 

[Sergei]

Doesn't "low pass filter" imply that there is something for it to pass? Isn't the idea of the missing fundamental effect that the brain 'hears' something that was never there in the first place? It isn't filtering something, but is synthesising a perception of something.

Oh, in this sense, yes, I agree - it would not be literally a LPF. What I meant was: wide-band-signal => some kind of "LPF" => low-frequency. Curious to hear what sound that toy actually emits, is it an "onion" or a "cake"

 

[solderdude]

I'll have my son try to locate it (ginormous task !) and probably need to put new batteries in.
Then will post a video of it.
Has nothing to do with MQA though.

 

[Sergei]

I'll have my son try to locate it (ginormous task !) and probably need to put new batteries in.
Then will post a video of it.

Thanks!

Has nothing to do with MQA though.

Demonstrates that we all can have a heated discussion about a thing most of us, including me, don't have complete information about.

Thinking literally though, yes, I agree, we strayed away from MQA. I guess the topic of MQA isn't that interesting anymore ...

 

[LTig]

As one of the criteria of accuracy, I suggested that a tweeter shall exhibit a meaningful response when the amplitude value changes from one 192 KHz sample to the next one - that is, its characteristic reaction time shall be 5.2 microseconds or less.

This is extremely hard to do (bandwidth of 192 kHz at least). Fortunately it is not required, since the bandwidth of 192 kHz PCM is 96 kHz. Which still is very hard to do.

In music signal components of lets say 90 kHz and above are very low in amplitude. A tweeter which is able able to emit such signals must have a frequency response of more than -3dB output level at 96 kHz.

 

[Blumlein 88]

I might complain how the thread has been completely destroyed regarding any relevance to MQA. But such illustrates why if you have to go to these crazy places to think MQA is good, well MQA is irrelevant itself.

So as someone posted Montgomery's law holds up just fine as an indicator of thread health.

 

[nscrivener]

Funny, I seem to be seeing connections where others don't. Strength or weakness? Maybe both.

Here's how I approach it: there is (very likely) a high-frequency PWM signal going to the piezo; there is a subjective sensation of low frequency sound => there got to be a mechanism effectively doing the job of LPF somewhere in between.

Whether it is through the missing fundamental effect, or through detecting fundamental frequency of the envelope of the higher-frequency amplitude-modulated carrier, or through some other mechanism, I don't know - I haven't heard this particular toy.

However, there doesn't appear to be an electronic or mechanical LPF in that part of the delivery chain, so the mechanism that does the job of LPF got to be biological.

A low pass filter is essentially a gate through which a signal passes, before the gate is a wider frequency range and after the gate frequencies above a certain threshold have been removed. You're talking about a process where the signal has been high pass filtered, but the brain fills in some of the missing low frequencies. There's simply no analogy here.

 

[amirm]

Additional reason for the subjectively perceived high accuracy of the high-end analog audio delivery chain can be explained by its high inherent temporal informational density, expressed in bits per second.

What are you talking about? Analog has been killed and buried by digital. Only uninformed, non-technical audiophiles cling to it. If analog had any virtues, this would not have been the outcome.

It may come as a shock to you but even multi-gigahertz radios now run in digital domain. The RF signal is digitized and demodulation occurs in software/DSP, allowing your mobile phone for example to support multiple concurrent standards.

There is not one paper advocating for superiority of analog being presented to our engineering societies.

Please stop this madness.

 

[Sergei]

What are you talking about? Analog has been killed and buried by digital. Only uninformed, non-technical audiophiles cling to it. If analog had any virtues, this would not have been the outcome.

It may come as a shock to you but even multi-gigahertz radios now run in digital domain. The RF signal is digitized and demodulation occurs in software/DSP, allowing your mobile phone for example to support multiple concurrent standards.

There is not one paper advocating for superiority of analog being presented to our engineering societies.

Please stop this madness.

I'm afraid I don't have power to stop it I was unaware of the phenomenon until last year, when I spoke with engineers at a recording studio in San Francisco. They retained their old LP master-cutting machine, and updated it with modern electronics. What got my attention was the waiting time for their LP-related services: as I recall, it was 7 months at that time! They were talking about expanding: they didn't have enough people trained in mixing and mastering for LP.

https://en.wikipedia.org/wiki/Vinyl_revival
"In its 'Shipment and Revenue Statistics' report for 2016, the Recording Industry Association of America noted that "Shipments of vinyl albums were up 4% to $430 million, and comprised 26% of total physical shipments at retail value – their highest share since 1985"".

https://www.classicfm.com/discover-music/millennials-are-going-nuts-for-vinyl-revival/
"Last year, more than 4 million chart-eligible LPs were sold in the UK alone – a remarkable increase from the 3.2 million records sold in 2016 – and this is expected to rise to around 4.5 million in 2019."

https://www.audioadvice.com/content/is-the-vinyl-revival-real-yes-and-heres-why/
"Vinyl record sales reached a 28-year high in 2015. At $416 million in sales, vinyl revenues actually surpassed those of all major ad-supported music streaming services combined."

 

[SIY]

Spotify alone (not even close to the larger players in the music delivery market)- $7B revenue last year. edit: total recorded music sales revenue is about $19B and change. LPs have surged to a massive 2.4% market share! I'd guess that the majority of sales these days are to the man-bun demographic.

Not that any of that is vaguely relevant, but there's some very dishonest number manipulation there. BTW, are you aware of how "modern electronics" in LP cutters work?

 

[Sergei]

A low pass filter is essentially a gate through which a signal passes, before the gate is a wider frequency range and after the gate frequencies above a certain threshold have been removed. You're talking about a process where the signal has been high pass filtered, but the brain fills in some of the missing low frequencies. There's simply no analogy here.

We are still talking about the toy here, right?

Even if it does use the missing fundamental effect, you'd still have to somehow extract the harmonics from the PWM signal that the piezo transducer emits. Then these harmonics will induce the illusion of the fundamental.

As I replied before, no - the missing fundamental effect by itself is not LPF. But it has to be fed by normal sinusoidal harmonics, which need to be recovered with the help of some LPF.

 

[amirm]

I'm afraid I don't have power to stop it I was unaware of the phenomenon until last year, when I spoke with engineers at a recording studio in San Francisco. They retained their old LP master-cutting machine, and updated it with modern electronics. What got my attention was the waiting time for their LP-related services: as I recall, it was 7 months at that time! They were talking about expanding: they didn't have enough people trained in mixing and mastering for LP.

Ask them how they record and mix their music and their most likely answer is digital. The format that loses timing resolution as you say. How do you think the LP puts that genie back in the box?

https://en.wikipedia.org/wiki/Vinyl_revival
"In its 'Shipment and Revenue Statistics' report for 2016, the Recording Industry Association of America noted that "Shipments of vinyl albums were up 4% to $430 million, and comprised 26% of total physical shipments at retail value – their highest share since 1985"".

By 1985 the LP was on its way to be buried. Here is the snapshot of formats as of last year:

LP is that tiny blip on top of the curve in navy blue. Overall market size was $10 Billion dollars and you get excited over 0.4 Billion?

Remember, a lot of LPs are sold because kids think it is cool, not because it has any fidelity advantage whatsoever. The audiophile market is tiny.

 

[Sergei]

Spotify alone (not even close to the larger players in the music delivery market)- $7B revenue last year.

Not that any of that is vaguely relevant, but there's some very dishonest number manipulation there. BTW, are you aware of how "modern electronics" in LP cutters work?

This is news to me that Spotify as a whole is among the major ad-supported music streaming services. I guess they were talking about services and service tiers like https://www.theverge.com/2019/4/18/18485804/amazon-music-ad-supported-free-tier-spotify-competition.

The point of the article relevant to me was: yes, vinyl is a niche market, yet not a market on the edge of oblivion, where the commonly shared belief puts it, and where it should be - if we believe the commonly used objective sound quality measurements. Why is this happening?

 

[Blumlein 88]

This is news to me that Spotify as a whole is among the major ad-supported music streaming services. I guess they were talking about services and service tiers like https://www.theverge.com/2019/4/18/18485804/amazon-music-ad-supported-free-tier-spotify-competition.

The point of the article relevant to me was: yes, vinyl is a niche market, yet not a market on the edge of oblivion, where the commonly shared belief puts it, and where it should be - if we believe the commonly used objective sound quality measurements. Why is this happening?

As Amir pointed out, most if not nearly all modern vinyl releases were recorded, mixed and mastered digitally. So the why is this happening isn't because of any temporal advantage you might think vinyl can possibly have. Which btw it doesn't have even when everything is analog all the way.

 

[Sergei]

This is extremely hard to do (bandwidth of 192 kHz at least). Fortunately it is not required, since the bandwidth of 192 kHz PCM is 96 kHz. Which still is very hard to do.

In music signal components of lets say 90 kHz and above are very low in amplitude. A tweeter which is able able to emit such signals must have a frequency response of more than -3dB output level at 96 kHz.

No, we don't need the sinusoids with frequencies over 20 KHz. We need pulses that can rise in 5 microseconds, and fall in 5 microseconds. Such pulses contain mechanical momentum that we want to reach the ears.

Let's take a tweeter capable of reproducing 20 KHz sinusoid at full amplitude. If it can truly track the analog signal in real time, this means that its diaphragm can go from zero displacement and zero velocity to full displacement in 12.5 microseconds. If we only need to go to 42% of amplitude for the pulse described above, such tweeter can reproduce the pulse too, because the tweeter's slew rate is high enough.

But a tweeter capable of reproducing 20 KHz sinusoid at full amplitude isn't necessarily capable of tracking the analog signal in real time. It may take its sweet time to get there, requiring multiple signal cycles to get to the full amplitude. Formally, it is rated up to 20 KHz, or maybe even up to 40 KHz. Yet it is not capable of reproducing the pulse.

 

[amirm]

No, we don't need the sinusoids with frequencies over 20 KHz. We need pulses that can rise in 5 microseconds, and fall in 5 microseconds. Such pulses contain mechanical momentum that we want to reach the ears.

Ah, no. Rise time of 5 microseconds translate into a bandwidth of 70 kHz.

 

[Sergei]

Ask them how they record and mix their music and their most likely answer is digital. The format that loses timing resolution as you say. How do you think the LP puts that genie back in the box?


By 1985 the LP was on its way to be buried. Here is the snapshot of formats as of last year:

LP is that tiny blip on top of the curve in navy blue. Overall market size was $10 Billion dollars and you get excited over 0.4 Billion?

Remember, a lot of LPs are sold because kids think it is cool, not because it has any fidelity advantage whatsoever. The audiophile market is tiny.

Nice graph. Why do kids think vinyl is cool? Maybe there is a fidelity advantage to them after all? It is reported anecdotally. Do you have references to research into this phenomenon?

Of course the LP shop mixes and masters digitally for LP. I heard about niche studios still mixing on tape for LP, for the "purity" of it, yet I haven't physically met engineers who still do that.

I don't remember what sampling rates that shop uses - I guess whatever clients give them? 192/24 is common these days. I do remember them saying that they don't have to downsample the final masters for the LP cutter, as they do for CDs. That was one of the reasons for the electronics update.

 

[RayDunzl]

It may come as a shock to you but even multi-gigahertz radios now run in digital domain.

No gigahertz here, at least until I see if the old Ham transceiver still works.

But 88~107mHz is used daily.

I bought an HDTuner a while back.

It allows me to specifiy either the primary analog or the digital sidebands (or just let it pick the better choice) for reception.

I wondered if it would send digits on the optical output when I selected Analog for the preferred reception mode.

It did. So I read up on modern FM devices.

Found that although it may look at the analog (traditional main broadcast) signal, it was still using DSP to demultiplex the signal and extract the content, therefore, digits were available for the optical out when the reception was "analog"...

That all became obvious when tuned to an older station without the Ibiquity HD add-ons, and digits still spewed from the ports.

---

Hmm...

I'll have to see if the analog reception has a greater bandwidth than the available compressed digital sidebands (not that I could hear it, but...)

 

[Sergei]

Ah, no. Rise time of 5 microseconds translate into a bandwidth of 70 kHz.

Couple of papers taking about the differences between the sinusoids and transients:

https://pdfs.semanticscholar.org/d2...3.1619984010.1561013925-1040519108.1558324547

https://pdfs.semanticscholar.org/b6...3.1619984010.1561013925-1040519108.1558324547

If you look at the graphs with extracted transients, you'll see that the transients are aperiodic and not symmetrical relative to the zero amplitude axis. As the papers say, trying to Fourier-transform them is not productive: it is much easier to treat them as signal components of a different kind.

We don't have to go far from your site to see examples of real-life signals recorded with higher than 44/16 resolution. For instance: https://www.audiosciencereview.com/...kris-dam1021-r2r-dac-measurements.2324/page-8.
Do you think the signals depicted in post #143 are naturally band-limited to 20 KHz?

If they were so band-limited, everything would be peachy. In my experience, cymbal signals usually aren't. Look at the signal #4 for instance. It starts with what looks like nine periods of a sinusoid. Try to imagine removing every three out of four samples, simulating the sampling at 44.1 KHz.

On this particular graph, the samples just happen to be captured in such a way that if you start removal from a certain point, then the signal sampled at 44.1 KHz, for these "nine periods", will almost disappear. The three samples taken out represent what I was talking about - rise and fall of a pulse. In this case, they are 5.7 microseconds apart.

You may argue: but the underlying signal corresponding to these "nine periods" is still there, look at the graph - it kinda reappears later. I would say: maybe, but the mechanical momentum corresponding to the "nine periods" wasn't transmitted to cochlea with the 44.1 KHz sampling on time, so the timing of the perception of the overall transient, even if it is eventually heard, is going to be off.

The sampling rate of 176,400 Hz appears to be adequate for this type of music signal. I can imagine how the reconstructed analog signal will approximate well the mechanical momentum transferred, and thus the transient will be heard at a time close to the time when it would be heard live, assuming same SPL for the live performance and reproduction from the captured PCM.