USB audio converters

[craiggsmith]

We got the following Sabrent device and used it today. I would assume it's the same as the one originally recommended, just with a nicer metal case and extension cable. But we still had distortion with louder speakers or those that were very close to the mic. Afterwards I tried to measure the output level with a DVM but couldn't get a good measurement; I might hook up a sine wave generator and measure it this week. For the last meeting I turned down the level on the mic mixer 5 db and there was only a slight bit of distortion with one person. But most of the people in that ward were farther from the mic, so I'll have to do more testing with other people this week.
https://www.amazon.com/gp/product/B00XM883BK

[russellhltn]

You might try digging into the control panel settings for the device. I didn't test extensively, but I think I got better results with AGC unchecked. I could not find any setting like "mic boost" I have with my built-in mic jack.

[CalS201]

We got the following Sabrent device and used it today. ........ But we still had distortion with louder speakers or those that were very close to the mic.

I have seen variation in signal level for RecordOut jacks in different bldgs. Some are 1v - 1.4v pk for a loud speaker. That's just too high for the USB adapter. You may have to add some attentuation like this -26dv pad https://www.amazon.com/Movo-MV-RC300-Mi ... 073HR6SY4/ and then readjust the computer's input gain. You could also use these volume controls - just realize the female TRS connectors are not the best quality! https://www.amazon.com/gp/product/B00001P4XH/ or https://www.amazon.com/gp/product/B071VL2GF8/

Afterwards I tried to measure the output level with a DVM but couldn't get a good measurement; I might hook up a sine wave generator and measure it this week.

You need to know the audio "peak" voltage - and keep the peak less then the maximum peak allowed by the USB input (0dbFS). A DVM typically only measures ac rms voltage. Furthemore, you have to be careful when using a sine wave as a substitute for human speech. The peak of a sinewave is 1.41 time higher than the rms , whereas the peak of human speech can be 10 higher then the rms value.

If you install and run a program like the free Audacity, or free ORBAN Loudness Meter, they can monitor the USB adapter input using their built in peak meters and easily tell you when you exceed the maximum pk value.

[russellhltn]

If you install and run a program like the free Audacity, or free ORBAN Loudness Meter, they can monitor the USB adapter input using their built in peak meters and easily tell you when you exceed the maximum pk value.

What's the trick with Audacity? I can see when I overload the recording level, but it doesn't necessarily tell me when I overload the input device.

[craiggsmith]

You might try digging into the control panel settings for the device. I didn't test extensively, but I think I got better results with AGC unchecked. I could not find any setting like "mic boost" I have with my built-in mic jack.

I tested today but forgot to do this, I'll check next time.

[CalS201]

If you install and run a program like the free Audacity, or free ORBAN Loudness Meter, they can monitor the USB adapter input using their built in peak meters and easily tell you when you exceed the maximum pk value.

What's the trick with Audacity? I can see when I overload the recording level, but it doesn't necessarily tell me when I overload the input device.

The recording level in Audacity controls the INPUT audio device VolumeLevel setting on the ControlPanel of the computer. If you connect a variable sinewave source to the USB adapter and slowly raise the amplitude, at some point the Audacity input "peak" meter will reach 0dbFS, which is the point of overload/distortion. This can be confirmed using the free "Orban Loudness Meter" program. You can also confirm it with the free"TrueRTA" audio o'scope program that shows the top of the sinewave going flat. Changing the Audacity recording level (or VolumeLevel on ControlPanel) is similar to adjusting the input channel "gain" on a mixer. Finally, if you put an rms DVM on the sine wave source you can read the rms and calculate the peak.

This link explains it better and has a table showing the maximum peak input for ControlPanel settings of 60% to 100%. Also, turning off AGC is a must!
viewtopic.php?f=27&t=37779#p216128

[craiggsmith]

I have seen variation in signal level for RecordOut jacks in different bldgs. Some are 1v - 1.4v pk for a loud speaker. That's just too high for the USB adapter. You may have to add some attenuation like this -26dv pad https://www.amazon.com/Movo-MV-RC300-Mi ... 073HR6SY4/ and then readjust the computer's input gain. You could also use these volume controls - just realize the female TRS connectors are not the best quality! https://www.amazon.com/gp/product/B00001P4XH/ or https://www.amazon.com/gp/product/B071VL2GF8/

I like the ability to monitor the signal with the pad, but it's a bit pricey. I was looking for something with a volume control before, but at this point I would be more inclined to try either the Headset Buddy or that line level USB adapter I found.

You need to know the audio "peak" voltage - and keep the peak less then the maximum peak allowed by the USB input (0dbFS). A DVM typically only measures ac rms voltage. Furthemore, you have to be careful when using a sine wave as a substitute for human speech. The peak of a sinewave is 1.41 time higher than the rms , whereas the peak of human speech can be 10 higher then the rms value.

Thanks, yeah, mine only measures rms, it's 30 years old so I was thinking of trying to find a new one that could measure peaks but probably not worth it. I saw up to 700mv with a sine wave so basically 1V. I had my wife sing and she could generate about half that but that's louder than anyone would speak. For now I lowered the input by 10db so we'll see how that goes. I did a test broadcast speaking into the mic very closely and still generated a little distortion, but most people wouldn't be that close. I should have done a test broadcast with different levels of the sine wave to see if I could measure the max input.

If you install and run a program like the free Audacity, or free ORBAN Loudness Meter, they can monitor the USB adapter input using their built in peak meters and easily tell you when you exceed the maximum pk value.

Interesting, I'll have to try that.

[craiggsmith]

Thank you very much to CalS201 who met up with me and tested everything. I didn't realize the computer's mic level setting would actually control an external USB converter. We found we had to lower it considerably, our record out jack is pretty hot. We have an old analog system and have access to change both the mic input level as well as the aux output level, and ended up dropping it 20 db (which is consistent with other posts here). I have instructed those doing the broadcast to keep the OBS level at max and watch the meter; if it gets into the red they adjust the computer's mic level, not the OBS level. We did a test with each computer to set the nominal level and so far only one person has had to adjust it a little since. We don't have an organ feed so the organ volume is a little soft at times, and you hear the people on the rostrum singing, but otherwise the audio quality is excellent.

[CalS201]

Craig, It was a pleasure to meet and help you solve those dastardly audio issues!

If there are others within 20-30 minutes of Herriman, UT that have not been able to solve their audio issues - I am happy to meet up at your bldg with my diagnostic equipment and hopefully together we can get you "pristine" audio! Just email me at cal.stanger@gmail.com