# I don't understand this 6 dB gain

**URL:** <https://forum.quantasylum.com/t/i-dont-understand-this-6-db-gain/1256>\
**Category:** QA40x\
**Created:** [February 25, 2024, 10:24am UTC](https://forum.quantasylum.com/t/i-dont-understand-this-6-db-gain/1256 "2024-02-25T10:24:17Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![sten](https://avatars.discourse-cdn.com/v4/letter/s/73ab20/32.png) [@sten](https://forum.quantasylum.com/u/sten)\
**Post date:** [February 25, 2024, 10:24am UTC](https://forum.quantasylum.com/t/i-dont-understand-this-6-db-gain/1256/1 "2024-02-25T10:24:17Z")

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Hi all

I am running the QA40x software version 1.194 on Linux with Mono. In this self-test, I am shorting the left inputs and outputs. According to the measurements, I’m outputting a sine wave of amplitude -6 dbV, yet the diagram shows 0 dbV and consequently the gain measurement shows 6 dB:

 ![Screenshot_2024-02-25_11-08-43](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/3/309a8d3e2045d3fcced8c13eb79c6db644673856.png)

Now you may think that this is because I specified an external gain of 6 dB, but that it not so, as you can see here:

 ![Screenshot_2024-02-25_11-09-08](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/4/418f0ca0b5b8b665196aad7f1ad0cb647796d921.png)

I don’t understand this behaviour. Could someone explain?

Cheers

Stephan

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**Author:** ![MarkT](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@MarkT](https://forum.quantasylum.com/u/MarkT)\
**Post date:** [February 25, 2024, 10:30am UTC](https://forum.quantasylum.com/t/i-dont-understand-this-6-db-gain/1256/2 "2024-02-25T10:30:56Z")

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The output level is given for a single-ended output - if you use full differential output you’ll see twice the voltage, hence the apparent gain of 6dB.

In the (relatively common case) of using a single ended output into an amp and sensing the output differentially to output ground no correction is needed, which I think makes sense.

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**Author:** ![fabra](https://avatars.discourse-cdn.com/v4/letter/f/58956e/32.png) [@fabra](https://forum.quantasylum.com/u/fabra)\
**Post date:** [April 13, 2026, 5:10am UTC](https://forum.quantasylum.com/t/i-dont-understand-this-6-db-gain/1256/3 "2026-04-13T05:10:47Z")

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In professional audio balanced connections are very common. Typically we would expect a setting for balanced/unbalanced.  
It is understanadable to say the generator output is given for an unbalanced conenction. But then still the gain measurement doesn’t make sense.  
So overall some improvement is needed here.

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**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\
**Post date:** [April 13, 2026, 1:46pm UTC](https://forum.quantasylum.com/t/i-dont-understand-this-6-db-gain/1256/4 "2026-04-13T13:46:32Z")

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Hi @fabra, the correct way to fix this is to give balanced output (via XLR) and unbalanced output (via BNC). And then the hardware would “fix it” automatically depending on the connector you used.

But since the QA402 and QA403 don’t have the space for both XLR and BNC, you need to recognize when you are using the outputs in balanced fashion and press the 6.02 dB gain button:

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/3/35bd1c4751d9ed9940cb9f4a1351623646b5c55a.png)

And you’ll get a status reminder on the display, and then all the math works out. In the config below (balanced loopback), if you place a DVM across L+ and L- you’ll measure 1Vrms = 0 dBV and gain is correctly reported as 0 dB.

 ![image](https://canada1.discourse-cdn.com/flex032/uploads/quantasylum/original/2X/5/554e3f733eac0eaaf4c2126717ff018ab234bd00.png)