Measuring Audio Interface Outputs with Multimeter - Need help please

[Voltzs]

Hi everyone! I am new to the forum and so glad I found a place specialized in electronics!

I am calibrating my monitoring chain in my music studio and before doing so I wanted to confirm that the outputs of my pro audio interface are +4dBu when a -20 dBFS sine wave tone is played in my audio software.

I know that a +4dBu signal is equivalent to 1.23 Volts - what I am having trouble with is my multimeter (Voltcraft VC 130). I have attached a picture showing my settings and connections. I did read the manual but I only manage to get a reading showing '125' (no decimal point) when using the 'Diode' setting, not '1.23' Volts.

As you can see from the attached pic, when I have the sine wave playing and am connected to the TRS cable from the Interface's output I get a reading of 125 - if I increase the level of the sine wave to 0 dBFS the multimeter's display reads 280 so there is a direct increase occurring at the output of my interface.

I am just not sure if I am using the multimeter correctly? When I plugged the red cable into the 'V' input and set it to any of the Volt settings I didn't get any number/figures that made any sense or at all correlated to 1.23 Volts.

I'd be grateful for any and all tips! Thank you!!

[wasedadoc]

You do not use the diode setting of any multimeter to measure a voltage source.

You can try the AC volts setting but be aware that many digital multimeters do not give accurate measurements when the frequency is above a few hundred Hz.

Update:  I see that the most sensitive AC volts range of your meter is 200.  That is not sensitive enough for the signal level you want to measure.  You also need to understand the accuracy specifications.  Look at page 38 of the manual https://asset.conrad.com/media10/add/160267/c1/-/gl/001090519ML04/manual-1090519-voltcraft-vc130-1-handheld-multimeter-digital-cat-iii-250-v-display-counts-2000.pdf. On AC, 1.5% + 8.  On the 200 volt range that means the error can be 3 volts (1.5% of 200) plus 8 counts.  Total error can be 3.8 Volts.  Not much use when you are trying to measure less than 2 Volts.  And yes, even that only applies to 40-400 Hz.

[Voltzs]

Hi wasedadoc! Thanks for your reply - yeah, I was also trying to establish my Multimeter's freq response as in the manual it also showed the freq response for a more expensive model  something like 10Hz to 10mHz...

Just so I understand clearly, are you saying my multimeter is not capable of reading the voltage output of my converter or not capable of reading the 1kHz tone? Should I try sending out a 200Hz tone? And if so could you please advise me of the settings?

I thank you for your patience!!

[golden_labels]

The diode test is used to measure at what voltage a PN junction starts conducting. Using that feature makes no sense in your case.

You want to measure AC voltage. According to the VC-130 datasheet it has only two AC voltage ranges: 200V and 250V, to which you must feed 40Hz–400Hz sine wave. Unfortunately it seems that accuracy is not high enough to measure 1.23V. Even with the better 200V range it’s ±0.82V error, so 2/3 of your expected value.

I suppose you could build a circuit to record envelope of the signal (search for terms “envelope” and “circuit” for examples, preferrably with “op-amp”) and then use the more accurate 2V DC range. But then you still need some way to calibrate it, which creates a chicken and egg situation. Perhaps it will be simpler to buy a $5 DT-830? (edit: see posts below)

[wasedadoc]

Perhaps it will be simpler to buy a $5 DT-830?

A DT-830 is no better. Lowest AC volt range is 200.  Accuracy may be even worse than the Voltcraft.

[Voltzs]

Perhaps it will be simpler to buy a $5 DT-830?

A DT-830 is no better. Lowest AC volt range is 200.  Accuracy may be even worse than the Voltcraft.

My multimeter is not the cream of the crop but I paid 50 Euros for it - is what I am trying to test so advanced?

Can you recommend the cheapest multimeter capable of carrying out this test?

I only need it for this. Thanks for your help!

[golden_labels]

wasedadoc:
Why in my mind DT-830 had a 2V range? I am silly. Thanks for pointing that out, corrected my post.

Voltzs:
No, it’s by no means anything that advanced. I am surprised that a multimeter in 50€ price range has no lower ranges.

As for suggestions, wait for opinions of others.

Used Uni-T UT70A is the same price. Goes down to 200mV, and in the range you need (2V) has 0.8%+3mV accuracy. Uni-T UT890D+ (note the letter!), though I did not use it myself, claims to have 6V range with 1%+3mV accuracy at half that price. While ordering, pay attention to the exact model number and — if possible — ask if they have the specified range.

[Voltzs]

Thanks - are you sure the models you have suggested have a frequency range up to 2kHz?

[ledtester]

What frequencies do you want to perform the level test at?

If testing at < 1 kHz is ok then meters such as the Aneng 8008 or Aneng 870 will do the job. They are both inexpensive, have a lot of features and you can find a lot of posts about them on this forum. Note that they will measure in RMS so you will have to convert to peak voltage if that's what you want.

Another approach is to build a rectifier circuit like this one that appears on page 10 in the LM3915 datasheet:

https://www.electroschematics.com/wp-content/uploads/2010/02/LM3915.pdf



It has good linearity but it has an offset of about 300-400 mV. It would still give you a pretty good idea of your output level, especially relative output levels. A more sophisticated circuit could give you a more precise level measurement. With a rectifier circuit you wouldn't have to get a new multimeter.

A third option is to get a cheap hand-held oscilloscope like the DSO138. You should be able to find one for around $20 USD. They suck at being a general purpose oscilloscope, but they should be fine for just looking at audio signals. Note that if you have more money to spend on a hand-held scope there are much better options.

[Voltzs]

Thanks for the info - I would want to check a 1kHz tone.

I am not that handy and have no experience with electronics so a rectifier circuit seems (while interesting) not for me.

[wasedadoc]

I can second the Aneng 8008 or 8009.  I have one of each among my collection of approaching 20 multimeters!

[Voltzs]

I see in the manual it says 40 - 1kHz for AC Voltage? I am hoping this means it would be acceptable for my needs? I am a total beginner here.

Would I not also need to read DC voltage? For DC there is no info about freq range?

[agehall]

There is no frequency in DC, that is why there is no info on it…

[Voltzs]

Ah ha! Ok - always learning something new here! Ok, so for my purposes of measuring the voltage of a 1kHz Sine wave coming out of my interface's Outputs, the ANENG AN8008 would be able to accomplish this, correct?

Thanks for your patience!

[bdunham7]

Ok, so for my purposes of measuring the voltage of a 1kHz Sine wave coming out of my interface's Outputs, the ANENG AN8008 would be able to accomplish this, correct?

Maybe, but inexpensive on-chip TRMS systems typically perform worse than basic average-responding system and you don't need really need TRMS for your purpose.  My cheap-POS Harbor Freight meter (non-TRMS, not the free one) doesn't reach 10% error (~1 dB) until >6kHz.

 I don't know how accurate a $10 TRMS meter will be at 1kHz.  Since your pro audio equipment is likely pretty flat, you can try it at 100, 400 and 1000Hz to see how it responds.  Or, you could buy just a little bit better meter that will work over the entire audio range--perhaps it will come in handy in the future.

[TimFox]

OP:  are you looking for small differences between the voltage of different signals, or evaluating over a wide range of voltage?
This is a quantitative question.

[Voltzs]

Hi Tim! I am trying to establish if a -20 dBFS 1kHz sine wave is equal to +4dBu at my interface's outputs. The reason this is important to me is so I have gain stage my other analog gear down the line through to my speakers. I hope this answers your question?

[ledtester]

FWIW, here is a table of AC readings from my Aneng 8008. The input in each case is a sine wave of amplitude 1 V generated by an Analog Discovery.

Code: [Select]

Freq  V RMS
200 0.721
400 0.721
600 0.721
800 0.721
1000 0.721
1200 0.720
1400 0.718
1600 0.714
1800 0.707
2000 0.698
2200 0.684
2400 0.665
2600 0.642
2800 0.612
3000 0.576

It is evident there is a drop-off in the meter reading around 1 kHz.

[TimFox]

Hi Tim! I am trying to establish if a -20 dBFS 1kHz sine wave is equal to +4dBu at my interface's outputs. The reason this is important to me is so I have gain stage my other analog gear down the line through to my speakers. I hope this answers your question?

Yes, that means you want a reasonably accurate absolute measurement of a voltage (that should be +4 dBu = 1.23 V rms), when you set a control to -20 dB.
A decent voltmeter will have the required specifications to determine the accuracy at your frequency.

[wasedadoc]

FWIW, here is a table of AC readings from my Aneng 8008. The input in each case is a sine wave of amplitude 1 V generated by an Analog Discovery.

Code: [Select]

Freq  V RMS
200 0.721
400 0.721
600 0.721
800 0.721
1000 0.721
1200 0.720
1400 0.718
1600 0.714
1800 0.707
2000 0.698
2200 0.684
2400 0.665
2600 0.642
2800 0.612
3000 0.576

It is evident there is a drop-off in the meter reading around 1 kHz.

Relative to 1 kHz:
1600 Hz -0.08 dB
2000 Hz -0.3 dB
2400 Hz -0.7 dB
3000 Hz  -1.95 dB

[SmallCog]

Know anyone with one of these?

https://www.gwinstek.com/en-global/products/detail/GVT-427B_GVT-417B

(Type of instrument, not specific model although I'm sure it'd do what you need)

Mine is a HP I pulled out of an e-waste bin as some people assume anything with a needle on it is useless...

[EPAIII]

A multimeter is a general purpose instrument and not necessarily well suited for audio measurements. While it is true that the better multimeters will have scales/settings that can do this kind of work, there is no guarantee even for those models. The meter you have is a brand X and from the photo and other comments it is plain that it is not one that is up to this use. It appears to be OK for testing things like automotive, door bell, or perhaps home wiring.

I am not familiar with what is available in your country, but I would look for places that sell professional electronic test equipment, not just electrical equipment. Find one you can trust and tell them what you wish to do. There are good quality meters in a wide range of prices that will do what you want.

One final thought: I have spent many decades working as a professional radio/TV engineer. Much of the work I did was with analog meters with accuracy levels in the 2% to 5% range. There is nothing magic about one given audio level. Many systems can work almost equally well with levels that differ by 2 and even 4 or more times from the ideal level. Often it is MATCHING levels that are really important instead of a precise level. And even an inaccurate meter can be used to match levels.

[BeBuLamar]

For 50 euros I think you can buy a meter that can do what you want adequately. Not very high accuracy but at least one with a 2V AC range..
I have a Fluke 8050a DMM which I paid $25 for over 20 years ago would make reasonable accurate measurement for at 0.5% and 10 counts. It's a 4 1/2 digit meter.

[Voltzs]

I just ordered the Aneng 8008 - but as it only displays RMS voltage how would I calculate the Peak voltage which is what I need?

There are calculations online but math never being my strong suit, are a bit over my head - if someone would be so kind as to present me with a calculation in layman's terms I'd be grateful!

RMS Voltage (simple equation) = Peak Voltage 

I thank you all for your help and patience!

[DavidAlfa]

Generate a  50/60Hz signal, any multimeter will work perfectly as it's designed for it (AC mains).
Then as you say, adjust for 1.23V, multimeters read RMS voltage.