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Measurements never lie, but sometimes they can be an illusion...
- Thread starter GXAlan
- Start date
Ultrasonics can indeed intermod in your tweeters. Of course, it will have to be pretty high level to make audible intermod, and the tweeters have to respond up there. A lot of tweeters get pretty inductive and won't respond much beyond 20kHz. Also, a simple low pass filter will knock that stuff down if you're worried.
Sorry, but I have no clue what your point is and the amount of text is too much for me to read it all (>1500 words, equivalent to 6 pages if double-spaced). Measurements measure what you have it measure, if you want to include ultra-sonics in the measurements, then you can.
You say the point is not to just look at ultrasonics, but just in case it was, those are going to be super low in level to not even be getting 1W, your music needs content up there; Amir does test ultrasonic performance, typically for Class-D, checking how high in frequency and low in volume that ultrasonic switching frequency is. He did it for the PA5, you can compare it to your measurement:
If people only choose to look at a few of the measurements, that’s on them. Just like only buying a speaker based on its on-axis performance (if that is even available). Having a suite of data (charts please, using mostly numbers make it incredibly annoying, such as SoundStage’s amp testing).
You mean measuring distortion at 1kHz? If so, Stereophile (and others) have Amir beat by a few decades in terms of measuring that. I assume Amir isn’t even the first to try and rank/rate performance.
You say the point is not to just look at ultrasonics, but just in case it was, those are going to be super low in level to not even be getting 1W, your music needs content up there; Amir does test ultrasonic performance, typically for Class-D, checking how high in frequency and low in volume that ultrasonic switching frequency is. He did it for the PA5, you can compare it to your measurement:
If people only choose to look at a few of the measurements, that’s on them. Just like only buying a speaker based on its on-axis performance (if that is even available). Having a suite of data (charts please, using mostly numbers make it incredibly annoying, such as SoundStage’s amp testing).
You mean measuring distortion at 1kHz? If so, Stereophile (and others) have Amir beat by a few decades in terms of measuring that. I assume Amir isn’t even the first to try and rank/rate performance.
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The ultrasonic switching signal is not played by tweeters, let alone heard by us. It's power is too low to burn tweeters. No intermodulation has been measured so far.
It's all in the FAQ btw.
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It's all in the FAQ btw.
Class D FAQ
This topic is dedicated to Frequently Asked Questions about class D amplifiers. If you have been directed here the reason is that it is easier to concentrate the frequent answers here instead of repeating them in several topics. Q1: Class D power ratings cannot be true. How can these small and...
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- Thread Starter
- #6
I agree 100% with your comment. You just didn't read my post to appreciate that was the intent.
The call to action isn't about standardization, it's more about having more instruments in the hands of more people. Amir's Topping PA5 sample had no difference between the two channels. My sample purchased from Amazon.com had as much as 10 dB difference in the noise in the bass. We should never ignore the standard tests -- they're standards for good, sound reasons. But it doesn't mean that new tests aren't worth investigating. Tools from @pkane let us easily evaluate new tests.
Thank you for the clarification.
I am not so sure about the easily to be honest. More instruments in the hands of more people will also lead to more confusion.
Two points:
1. Topping was measuring audio gear well before I arrived. They run their own tests that are different than mine combined with what I run.
2. One channel having different noise level may very well be instrumentation. I routinely play with grounding only to have one channel get better and the other worse. You have to rule this out before blaming the audio device under test. I usually comment in my reviews about the efforts I put in to eliminate such noise issues.
1. Topping was measuring audio gear well before I arrived. They run their own tests that are different than mine combined with what I run.
2. One channel having different noise level may very well be instrumentation. I routinely play with grounding only to have one channel get better and the other worse. You have to rule this out before blaming the audio device under test. I usually comment in my reviews about the efforts I put in to eliminate such noise issues.
2: That's definitely worth investigating. My measurements of PA5 (also using Cosmos ADC) looked very noisy until I connected their grounds by a short, thick wire. The result was much cleaner then:
So which if the two has more ultrasonic noise again?
On this point, my measurements come at the product from many vantage points. It is exceedingly hard to cheat in a way that produces empty measurements with no value. There is no parallels here to video driver hacks you mentioned.
There are very special cases where audio equipment detects measurement equipment though: Chord for instance won’t output the impulse response of their DACs
- Thread Starter
- #14
I think the story telling aspect didn't work as intended -- I'm not saying any company is cheating. I'm the one that's being the magician and creating the illusion. I am saying that it's possible to present present data in the way that the storyteller (magician) wants while not lying by changing the way tests are run and presented.
Part two is that you can do really well with a 1 kHz test tone (and not do well with the multitone). You see that with the Marantz -- for 1 kHz, it doesn't have a lot of ultrasonics. For multitone, it's worse than the Topping.
Going forward, it's a good idea for more people to start testing themselves. As you understand the test parameters, we'll may come up with better tests.
(Edit: Without spoiling The Prestige (the 2006 movie), my story telling approach probably makes more sense if you watch the movie again).
valerianf
Addicted to Fun and Learning
As class D amps have ultrasonic noise it would be very useful to add some tests in the high frequencies range.
May be a TIM or THD around 10 khz.
Do somebody has an idea?
May be a TIM or THD around 10 khz.
Do somebody has an idea?
MaxwellsEq
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A real question to answer is whether ultrasonic, electronic noise matters. Clearly, there are no humans reliably able to hear sound above 20kHz, and if we're over 40 years old, hearing over 17kHz would be good.
Which is why the audio industry has used 20kHz as an upper limit for testing for decades.
There has, however, been an ongoing debate about wide bandwidth amplifiers for years. Some designers aim for a flat response to 50 or 100kHz. When TIM was first discovered, wide bandwidths were argued as essential to enable high slew-rates.
However, given the increasing amount of electronic noise, perhaps it is safer to reject anything outside the normal audio range in order to be confident that there is no location-specific interaction.
Which is why the audio industry has used 20kHz as an upper limit for testing for decades.
There has, however, been an ongoing debate about wide bandwidth amplifiers for years. Some designers aim for a flat response to 50 or 100kHz. When TIM was first discovered, wide bandwidths were argued as essential to enable high slew-rates.
However, given the increasing amount of electronic noise, perhaps it is safer to reject anything outside the normal audio range in order to be confident that there is no location-specific interaction.
You might not hear those sounds, but you can hear effects of band limiting. Fast attack has a lot of Fourier components. If you band limit that, then the attack gets smeared.
To me, the drumsticks hitting cymbals do sound different when listening on CD or LP/SACD. Or real life. Example: Police's "Message In A Bottle", Foo Fighters "Dear Rosemary".
That difference is audible ONLY if the recording master was originally analog, with lots of bandwidth. Or archived with high bandwidth. I saw a lot of "SACD" issues that are basically CD quality, brick walled at 20kHz. Foobar2000's "Spectrum" shows that clearly.
Example: Rush's "Moving Pictures" (even their DVD-A is limited at 17-18kHz). Sounds good, but something is missing from cymbals...
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Now... there is almost no "live" rock, pop, or other modern music. Everything we hear "live", in a concert, is piped trough microphones, transducers (guitar pickups) and speakers. Unplugged events sound different and are reserved only for a few people.
Unless you are listening to symphonic music, and even then, the room you listen has it's own characteristics.
The difference that I am talking about is based on analog bandwidth on those chains.
On Class D Amplifiers Measurements
I/O measurements of Hypex NC252MP step response/rise time and of input/output spectra with 20kHz square signal. Staying technical, showing parameters and behaviour. Not mentioning audibility. Step response 20kHz square I/O spectra (interesting output noise modulation) I’m amazed it’s that...
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