Author Topic: Anyone to make sound measurements with an oscilloscope?  (Read 2185 times)

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Offline Targhan

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I made a few discoveries while recording sounds from the CPC (through the stereo output, into a high-end sound card), and I'd like to confirm them thanks to the accuracy of an oscilloscope. Should you accept this mission, I would send you an executable on CPC to play some sounds, and if you could "record" what's going on on your oscilloscope, that would be great. I have no idea how you could conveniently show me the waves though. Maybe the stuff is now electronic and can produce nice waveforms at regular instants??? Forgive my lack of hardware knowledge, last time I used an oscilloscope was in high school :)

If these measures confirm my doubts, I'd be glad to share these info, which can be very useful for emulators and music software.

Thanks!
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Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #1 on: 13:00, 10 April 21 »
I can make a recording for you and send you the result in screenshots or data points which you can then analyse. You'll have to let me know what sample rate etc you need.


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Offline Targhan

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #2 on: 15:01, 10 April 21 »
PM sent. Thanks a lot!
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Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #3 on: 17:03, 10 April 21 »
Yup, sent you some questions back. Many things can be measured on a scope, so your answers will make the results as close as possible to what you need.

Bryce.

Offline RetroCPC

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #4 on: 01:27, 13 April 21 »
Hi Targhan,

I can run some FFT tests if you want - these can tell you more in the frequency domain then oscilloscope screenshots,

John

Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #5 on: 09:58, 13 April 21 »
I'm not sure he wants to go so deep as to investigate harmonics etc. But I can connect the CPC to a spectrum analyser too if needed.

Bryce.

Offline Targhan

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #6 on: 10:21, 13 April 21 »
I can run some FFT tests if you want - these can tell you more in the frequency domain then oscilloscope screenshots,
Thanks, but indeed that's not going to be useful to me. Bryce's measures will be enough :). But I think I already know the result before even seeing it.
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Offline roudoudou

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #7 on: 10:27, 13 April 21 »

it will be useful for a proper replay
i did some "measures" back in time but it was with a soundcard sooooo i guess there was an hardware filter
i guess that square generation is all but squared :D
use RASM, the best assembler ever made :p

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Offline RetroCPC

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #8 on: 11:56, 13 April 21 »
i guess that square generation is all but squared :D


Oh man thats for sure :)

The CPC "Whine" from internal speaker is part due to Clock Phase Noise from the ULA + poor Grounding and PSU (both of which will result in poor phase noise as well as directly modulating the audio B/W).
« Last Edit: 11:59, 13 April 21 by RetroCPC »

Offline GUNHED

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #9 on: 15:54, 13 April 21 »
...I can connect the CPC to a spectrum analyser...


The CPC is analysing the speccy, what will be the outcome?  :laugh: :) :)
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Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #10 on: 16:39, 13 April 21 »

The CPC is analysing the speccy, what will be the outcome?  :laugh: :) :)

It's a different spectrum - Faster and no colour clash. :) (although it does have rubber buttons).


Bryce,

Offline stevensixkiller

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #11 on: 02:16, 15 April 21 »
You need a sample rate higher than 48Khz?
I'm not a specialist but some project like MDFourier http://junkerhq.net/MDFourier/mdfourier.html that work on emulator sound accuracy just need recordings of OG hardware with an external audio soundcard to make comparisons.

Offline GUNHED

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #12 on: 03:24, 15 April 21 »
Can't wait to see some pictures of "what's really coming out" at the sound channel(s)
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Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #13 on: 10:14, 15 April 21 »
You need a sample rate higher than 48Khz?
I'm not a specialist but some project like MDFourier http://junkerhq.net/MDFourier/mdfourier.html that work on emulator sound accuracy just need recordings of OG hardware with an external audio soundcard to make comparisons.

I can sample at up to 2Ghz.

McBryce.

Offline Targhan

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #14 on: 12:52, 15 April 21 »
Can't wait to see some pictures of "what's really coming out" at the sound channel(s)
You can still have the results done by SuperSylvestre.

I just needed more tests, hence my post.
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Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #15 on: 14:04, 15 April 21 »
I'll try to get the tests done at the weekend. Unfortunately my "Retro-Desk" is currently my home office desk so I don't have the space during the week to set it up.

Bryce.

Offline roudoudou

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #16 on: 14:07, 15 April 21 »
You can still have the results done by SuperSylvestre.

I just needed more tests, hence my post.
signals from AY chip or from a channel after amplification?
anyway, it's obvious 44KHz or 48KHz replay is not enough for CPC emulators
Did you allow Arkos tracker to use 192KHz replay when available?
use RASM, the best assembler ever made :p

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Offline Targhan

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #17 on: 14:10, 15 April 21 »
Did you allow Arkos tracker to use 192KHz replay when available?
No filter on what frequencies to use is done, so yes. But I'm not sure you can make the difference, really :).

I'll try to get the tests done at the weekend.
Thanks. I'm not pressuring you :).
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Offline roudoudou

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #18 on: 14:14, 15 April 21 »
No filter on what frequencies to use is done, so yes. But I'm not sure you can make the difference, really :) .
Thanks. I'm not pressuring you :) .
a SOUND 1,7 at 44/48Khz and 192KHz, the difference is obvious, the harmonics too :D
ok, that's not a usual sound
use RASM, the best assembler ever made :p

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Offline Targhan

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #19 on: 14:19, 15 April 21 »
You don't even hear it on a real CPC either!
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Offline roudoudou

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #20 on: 14:21, 15 April 21 »
You don't even hear it on a real CPC either!
sound 1,7 is still clear for ME on a real CPC
at my age sound 1,5 is too high-pitched but i remember when i was young, up to SOUND 1,3 :D
are you still ok? =>
https://www.youtube.com/watch?v=qNf9nzvnd1k
use RASM, the best assembler ever made :p

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Offline Targhan

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #21 on: 14:30, 15 April 21 »
On the CPC speaker? I *think* I hear something at 1,5, but there's so many glitch it could be anything. Even a FOR loop in Basic produces sound, so what you hear with the SOUND command is really biased.
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Offline GUNHED

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #22 on: 17:30, 15 April 21 »
sound 1,7 is still clear for ME on a real CPC
Same here, for sound 1,6 I do need external speakers though.
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Offline BSC

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #23 on: 22:29, 15 April 21 »
If these measures confirm my doubts, I'd be glad to share these info, which can be very useful for emulators and music software.

Very interesting topic! Looking forward to what you will be sharing.

PS: SOUND 2,7 here (it's easier in stereo)

Online Bryce

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Re: Anyone to make sound measurements with an oscilloscope?
« Reply #24 on: 17:11, 17 April 21 »
Why does the program crash the CPC and mess up the screen? Is that correct? Surely you could have just created those sounds in BASIC?

Bryce.

Edit: Ok, I'm going to need a better program to work with. I need each tone in a separate file and it should repeat when I press the space bar or some other key (or be continuous. Otherwise this test could take days to complete.
« Last Edit: 17:34, 17 April 21 by Bryce »