The Shower Test - can you spot PWM?

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DavidEF
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Scallywag wrote:

DavidEF wrote:
Well, most sound cards now can do at least 48khz and there are sound cards capable of 192khz for professional use. They don’t look or act like what most people think of “sound cards” but still… Big Smile

Right, but before I buy a 192KHz sound card, I’m buying a $20 DMM and a photodiode or LED or solar cell (or all three)


Okay actually I found a $40 sound card that claims something to do with 192KHz, but that was also admittedly a very quick google search.


Well, “Pro” sound cards capable of 192khz have been around long enough that I wouldn’t doubt you could get a “consumer” grade one now with that high frequency. I haven’t tried looking. But since mobos come with 48khz, 7.1 channel, surround sound on-board, the standalone cards would need to have some feature that the mobo chips don’t yet have. It would make perfect sense.

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ToyKeeper
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DavidEF wrote:
since mobos come with 48khz, 7.1 channel, surround sound on-board, the standalone cards would need to have some feature that the mobo chips don’t yet have. It would make perfect sense.

The main features in add-on sound cards are a better signal-to-noise ratio, more recording channels, studio monitor ports, more types of plugs, mixer controls, phantom power for mics, line-level adjustments, preamps, lower latency, and things otherwise intended to make music production easier or higher-quality. Usually they’re called audio interfaces.

For example, the Arturia Audiofuse is popular lately. Another nice one is the Sound Devices MixPre-10M.

maukka
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Audio spectrum analyzers work fine for figuring out the PWM frequency. Here’s two programs I regularly use: REW and ARTA.

I used an M-Audio audio interface connected to a Thorlabs photosensor.

AEDe
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Funny pics.I never look at such big drop to see such oscillations. Very interesting effect. Thanks for the information.
Usually I look at many small drops far from origin (1-1.5m) in such way PWM up to 20-25KHz can be seen. Low PWM frequency <5kHz , I can see “directly” by eye movement.

For me minimum comfort frequency which I don’t notice at real using is about 10KHz.

maukka
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AEDe wrote:
For me minimum comfort frequency which I don’t notice at real using is about 10KHz.

I’ve done some tests with a function generator and 8kHz is usually fast enough for me. The limit depends on the duty cycle, but 10kHz seems a safe minimum for me too.

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AEDe wrote:
Funny pics.I never look at such big drop to see such oscillations.

It may not be obvious from the picture, but the drops aren’t big. The big one on the left with a dotted line next to a streak was only about a millimeter in size. The smaller one at the top of the right image, also showing a dotted line effect, was maybe a tenth of a millimeter wide. This was taken very very close to the stream. The visible part of the shower head is only about 1cm. Most of the drops are moving faster than terminal velocity, and they slow down as they fall.

AEDe wrote:
For me minimum comfort frequency which I don’t notice at real using is about 10KHz.

Same here. I find PWM distracting during use if it’s slower than 10 kHz. Above that is comfortable though.

AEDe
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ToyKeeper wrote:

The big one on the left with a dotted line next to a streak was only about a millimeter in size. The smaller one at the top of the right image, also showing a dotted line effect, was maybe a tenth of a millimeter wide. This was taken very very close to the stream. The visible part of the shower head is only about 1cm. Most of the drops are moving faster than terminal velocity, and they slow down as they fall.


Oh thanks,I see. It is not big , but close to shower head. For small drops “relaxation paths” should be smaller, than for big one.
Scallywag
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I will occasionally hear PWM that I can't see, so I'd like to keep it above ~18KHz just in case. 

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So as not to hijack this thread,
I did a post about using Audio software to measure PWM Frequency:
http://budgetlightforum.com/node/67220

joechina
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ToyKeeper wrote:
gchart wrote:
My el-cheapo DMM (ZT102) has frequency and duty cycle functions and they seem to do pretty good. I was pretty impressed. Kinda handy when doing driver dev and testing.

Oh, nice. My cheap DMM doesn’t do that… maybe I should get one of those instead. Smile

I just bought one of this cheap multimeters because you mentioned the ZT102 for duty cycle measurements, but there are more interesting ones.

Like the AN8009
http://budgetlightforum.com/node/57714
Has a µA range,
ca. $25
Safety is not good because of a wrong CAT rating, like all cheap ones.

I sniffed around and found the
ANENG AN870
This has a 10mA range (the AN8009 miss this)
Has everything was the smaller ones have and runs on AA
$26 in the Ali-App and a coupon brought it down to $22
And suddenly my credit card was charged.
Damn! I need a new meter as much I need a new light.
https://m.aliexpress.com/item/33004463675.html

HKJ tested a lot of nice cheap DMMs
Most of the new ZT Zotek or AN Aneng have a duty cycle.
http://lygte-info.dk/info/DMMReviews.html

A nice geek DMM is the 121GW from the eevBlog. It costs a bit more.
https://lygte-info.dk/review/DMMEEVBlog%20121GW%20UK.html

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