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#50 Reply
Posted by
David Hess
on 30 Nov, 2022 16:54
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Now I want to convert the 0.754 RMS signal to Peak.
Press the following keys on your calculator:
0.754 x 1.414 =
But why do you want the peak value? I don't think it has any meaning in your context.
The peak value is needed to prevent clipping.
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#51 Reply
Posted by
wasedadoc
on 30 Nov, 2022 17:09
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Now I want to convert the 0.754 RMS signal to Peak.
Press the following keys on your calculator:
0.754 x 1.414 =
But why do you want the peak value? I don't think it has any meaning in your context.
The peak value is needed to prevent clipping.
But as already explained in an earlier post in this topic, "peak" in the context of audio level frequently does not mean 1.414 times RMS. For example when recording on an audio cassette deck, one would be adjusting the input level control to have the VU meters peak at, say, 0dB. Yes, to avoid distortion but the VU meters already took the RMS versus maximum voltage excursion into account.
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#52 Reply
Posted by
David Hess
on 30 Nov, 2022 18:05
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But as already explained in an earlier post in this topic, "peak" in the context of audio level frequently does not mean 1.414 times RMS. For example when recording on an audio cassette deck, one would be adjusting the input level control to have the VU meters peak at, say, 0dB. Yes, to avoid distortion but the VU meters already took the RMS versus maximum voltage excursion into account.
I agree, but if testing with sine waves, it is still useful to know the peak value after making an RMS measurement.
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#53 Reply
Posted by
Voltzs
on 30 Nov, 2022 18:26
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Many thanks for the replies!
As my initial goal was to establish what dBFS value in my DAW produced +4dBu at my interface's Outputs, I measured 1.915 VRMS with a -20dBFS 1kHz sine wave.
I know that my meter has, according to its manual, a +/- 1.0%+3 - so I am wondering if this is why my meter does not read 1.228 VRMS?
As I have no previous experience with these measurements, is a reading of 1.915 VRMS (when the signal is technically 1.228 VRMS) close enough to be considered accurate - again, taking into account the meters +/- discrepancy?
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#54 Reply
Posted by
bdunham7
on 30 Nov, 2022 18:46
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I know that my meter has, according to its manual, a +/- 1.0%+3 - so I am wondering if this is why my meter does not read 1.228 VRMS?
As I have no previous experience with these measurements, is a reading of 1.915 VRMS (when the signal is technically 1.228 VRMS) close enough to be considered accurate - again, taking into account the meters +/- discrepancy?
No, your specification means that the reading should be off by no more that 1% of the reading (0.019V) plus 3 counts of your meter, which should mean 0.003V if it is in the 10.000V range. So +/- 0.022V would be the maximum expected error. So something is way off.
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#55 Reply
Posted by
Kleinstein
on 30 Nov, 2022 18:49
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1.23 V and 1.92 V are quite different - more than 30% or some 3 dB off. So the meter should not be that inaccurate. A common problem is that frequency generators usually specify there output amplitude when loaded (e.g. 50 Ohm or sometimes 600 ohm). There could also be some confusion the full scale range, this may be in volts peak and not RMS.
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#56 Reply
Posted by
Voltzs
on 30 Nov, 2022 19:29
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Hi Klenstein - thanks for your reply - I think the confusion might be because of how I read my multimeter:
There are 3 'range' options when reading a signal:
When I used the first range option the meter read 1.915 - the 2nd range option read 0.1.19 - and the 3rd read 001.9
I think the accurate reading is 0.1.19 VRMS, right? I am not skilled with these types of things - learning by doing. Haha
0.1.19 VRMS would of course be much closer to 1.23 VRMS which is equivalent to +4dBu.
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#57 Reply
Posted by
Kleinstein
on 30 Nov, 2022 20:05
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One may have to check if the meter reads the AC part only or also reacts to an DC offset. Some meter react also to DC, especially in the mV range. The higher voltage ranges could be different.
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#58 Reply
Posted by
bdunham7
on 30 Nov, 2022 20:40
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When I used the first range option the meter read 1.915 - the 2nd range option read 0.1.19 - and the 3rd read 001.9
I think the accurate reading is 0.1.19 VRMS, right? I am not skilled with these types of things - learning by doing. Haha
I can't see what I need to in your picture, but I'm afraid the most likely reason for your results is that your new meter is either a complete POS or is somehow unsuited for this job. There shouldn't be a DC offset on an audio output--something is broken if there is--but the symbols on the Aneng 8008 may indicate that it does not have AC coupling at all. Does anyone have one that can check for the OP? In any case, one way to quickly test a meter is to compare its ranges against each other. Reading 1.915 V on the 10.000V range and then 1.19 on the 100V range is not good. I don't know what is going on there.
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#59 Reply
Posted by
Voltzs
on 30 Nov, 2022 21:03
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With regards to the 'Range' function, the manual says:
'RANGE: press this button to enter the manual range; each push increases the range; when the highest range is reached, next push will go back to the lowest range.
On the middle range setting I had the reading of 0.1.19 VRMS
As far as the display goes - all that is seen on the lefthand side is 'AC' because that is what I set the meter to.
Considering I am trying to establish if -20dBFS = +4dBu at my Interfaces's Outputs, couldn't one 'reasonably' assume that -20dBFS giving a reading of 0.1.19 VRMS is close enough to 1.23 to say, 'yeah, -20 dBFS = +4dBu?
Thanks for your patience!
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#60 Reply
Posted by
bdunham7
on 30 Nov, 2022 21:39
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On the middle range setting I had the reading of 0.1.19 VRMS
According to what I can find (excerpt attached) your VAC function has three ranges, apparently only indicated by the decimal point. You are listing two decimal points in 0.1.19, so that isn't helpful and shouldn't be what you are seeing--is it? Anyhow, the meter has 10,000 'counts', from 0 to 9999. The ranges are 9.999V, 99.99V and 750.0 (limited by things other than the ADC). You typically want to take your measurement with the lowest range possible for best accuracy, so in this case it would be the lowest of the VAC ranges--9.999V. However, this reading should be pretty consistent with higher ranges, so if you have 1.915V on the 9.999V range, you really ought to have 01.9x in the 99.99V range, the 'x' being the only digit that would vary much. If you don't something is wrong.
b/t/w--does it really not suppress the leading zero? Can you post good photos taking those two measurements?
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#61 Reply
Posted by
BeBuLamar
on 30 Nov, 2022 21:43
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I know that 1dBu = 0.775 volts
I thank you for your patience! 
0.775 Volts is 0dBu not 1dBu.
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#62 Reply
Posted by
Brianf
on 01 Dec, 2022 07:16
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As my initial goal was to establish what dBFS value in my DAW produced +4dBu at my interface's Outputs, I measured 1.915 VRMS with a -20dBFS 1kHz sine wave.
...so I am wondering if this is why my meter does not read 1.228 VRMS?
-20dBFS giving a reading of 1.915 FOR YOUR EQUIPMENT is correct. A different piece of equipment might generate 0.775VRMS, another might generate 100VRMS. It depends on the equipment.
dBFS is simply a measure of how far away from digital clipping you are.
It has no equivalent voltage level.If you really want your setup, when outputting at -20dBFS, to make an analogue signal of +4dBu then you will need to attenuate the 1.915VRMS down to 1.228VRMS.
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#63 Reply
Posted by
wasedadoc
on 01 Dec, 2022 09:57
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You will get best accuracy from the meter by letting it autorange. And I doubt it ever shows 2 decimal points on any range in any mode.
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#64 Reply
Posted by
Voltzs
on 01 Dec, 2022 10:12
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Thanks for your reply.
I hope the attached image is more clear for you. When I power the multimeter on I switch it to V, then press the orange select button to toggle into AC mode, and the first reading can be seen on the image to the L - the Middle image is the second 'range' option, and the third is the one that shows 00.13 (although to be specific, the '3' is not solid, it toggles constantly between 1,2&3.
I hope this sheds light on the Multimeters behavior.
As mentioned already, can one take a 01.19 VRMS reading and deduce it is a measurement of 1.23 VRMS being that it is so close and taking into account the cable used or the meter not being 100% accurate? Because I do not need 100% accurate - I just wanted to establish whether a -20dBFS 1kHz sine wave is equal to +4dBu.
As an experiment I changed the -20dBFS to -19.77 dBFS and got a 1.277 VMRS reading.
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#65 Reply
Posted by
Brianf
on 01 Dec, 2022 10:21
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I just wanted to establish whether a -20dBFS 1kHz sine wave is equal to +4dBu.
Why do you think that it ought to be?
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#66 Reply
Posted by
Voltzs
on 01 Dec, 2022 10:29
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Hi Brian - asking questions rather than answering them is really frustrating - have you read this thread from the very beginning? If you did then you would know I am gain staging my analog recording equipment and want to properly match all my output to input levels, in particular my monitoring setup. I will not repeat that all again. You are not helping me gain clarity here.
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#67 Reply
Posted by
JohanH
on 01 Dec, 2022 11:25
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I think there is some confusion here (or you aren't reading the meter correctly). When and where did you get the 1.915 V reading? The three pictures shown:
1.195 V
01.19 V
001.3 V
These readings are the same, they just vary in resolution of the meter. The first reading is correct and most accurate. Use the Auto setting.
1.195 V could be rounded to 1.20 V (with two digits) and that's not far from your expected 1.23 V.
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#68 Reply
Posted by
Brianf
on 01 Dec, 2022 11:32
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Hi Brian - asking questions rather than answering them is really frustrating - have you read this thread from the very beginning?...
Yes I have, and I have many many years experience in professional audio engineering BUT I still see nowhere above that explains why you believe that a signal originated at -20dBFS will give you an analogue signal of +4dBu for your interface.
If you read my reply here...
https://www.eevblog.com/forum/beginners/measuring-audio-interface-outputs-with-multimeter-need-some-guidance/msg4555184/#msg4555184...you will see that I point out that there is no correlation between dBFS and dBu and that it depends on the equipment under test.
All you can do is generate a signal at -20dBFS and measure the analogue signal generated. The voltage generated is the correct answer. If that happens to be +4dBu then happy days. If it isn't, and if it is important that it is, then you will need to either attenuate it or amplify it before passing it down the chain.
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#69 Reply
Posted by
BeBuLamar
on 01 Dec, 2022 12:45
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I think you expect too much. 1.19V with 3% accuracy can be 1.23V. Also the audio interface if it actually put out 1.19V is close enough.
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#70 Reply
Posted by
wasedadoc
on 01 Dec, 2022 13:02
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The spec for the Aneng 8008 on AC voltage is +/-(1.0%+3) 40Hz-1kHz. With an input between 1 volt and 10 volts RMS it will auto select the 9.999 Volt (ie 10) range. The % applies to the FSD. Full Scale Deflection is a hangover from analogue days and translates to the maximum of the selected range for a digital meter. The '3' is the error in the final digit. So the bound on the total error is 1% of 10 volts plus 0.003. That is 0.103. Means if the input is exactly 1.230 the meter could show any number between 1.127 and 1.333.
In dB terms that uncertainty is less than 0.8dB.
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you're needs to measure Voltage when signal output is connected to your equipment audio input. Otherwise you're needs to measure it's impedance and use the same dummy load. Usually audio impedance is about 600 Ω, but not always. Some equipment may have different impedance.
Note, that there is different Voltage when output is open and when output is connected to some audio input. And that Voltage drop depends on the load impedance.
Regarding to your DMM, you can check it's RMS or Peak Voltage measurement with signal generator. Just setup some known Voltage on the signal generator and test your DMM. And again don't forgot to put proper termination load, because open output will have twice higher Voltage than output with proper load.
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#72 Reply
Posted by
Brianf
on 01 Dec, 2022 16:11
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Usually audio impedance is about 600 Ω, but not always. Some equipment may have different impedance.
No, it's not and hasn't been since some time in the last century.
Modern equipment (anything designed since the early '80s) is designed to have a low output impedance and a high input impedance. The screenshot the OP posted shows that their equipment has an output impedance of 56R and an input impedance of 11k2.
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#73 Reply
Posted by
TimFox
on 01 Dec, 2022 16:40
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"Regarding to your DMM, you can check it's RMS or Peak Voltage measurement with signal generator. Just setup some known Voltage on the signal generator and test your DMM."
I have not seen a modern AC voltmeter that measured peak voltage, or was not calibrated in V RMS.
Some are "average responding" and the calibration converts the mean absolute value measured by the circuit to RMS voltage, assuming a sine wave.
Others are "true RMS" and measure the RMS voltage directly, within limits for crest factor, etc.
The old vacuum-tube analog voltmeters ("VTVM") often used a 6AL5 voltage doubler that actually measured peak-to-peak voltage.
The moving-pointer meter would then have two scales: peak-to-peak voltage, and RMS voltage (where the calibration again assumed a sine wave).
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#74 Reply
Posted by
BeBuLamar
on 01 Dec, 2022 17:11
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I have not seen a modern AC voltmeter that measured peak voltage, or was not calibrated in V RMS.
Some are "average responding" and the calibration converts the mean absolute value measured by the circuit to RMS voltage, assuming a sine wave.
Others are "true RMS" and measure the RMS voltage directly, within limits for crest factor, etc.
While it can't measure the peak voltage of a 1000Hz sine wave something like the Fluke 289 can measure the peak voltage of a 60Hz AC voltage with decent accuracy.