Using Autoranging to Maximize SNR

Additional Resources for SoundCheck

Detailed explanations of how to use SoundCheck can be found in the SoundCheck manual.

Video Transcript: Using Autoranging to Maximize SNR

When you’re making measurements in SoundCheck, it’s important to have the best signal to noise ratio possible. Let’s look at some tools that can help improve this.

Whenever an acquisition step runs in SoundCheck, it outputs a value called the Max FSD in. FSD stands for “full scale deflection”

I run the sequence, and I can look at the Max FSD value here. This value shows how much of the input signal you are using. For example, if the Y value was 0 dB FSD then it is using all of the bits in the input of the A to D converter on the input.  Anything above 0 would be clipping. Ideally we want this number to be between -30 and 0 to get a good single to noise ratio without clipping our inputs. 

There’s a few ways we can do this. 

• We can increase the stimulus level. 
• We could move the device under test and the microphone closer. 
• We could reduce the noise of our environment
• And we could add input gain on our audio interface, if that option is available.

If you’re using Listen Hardware, you can automatically read the gain on the channel in the calibration settings.

I’m using an AmpConnect 621, my reference microphone is connected to input 1, and the gain is set to 0 dB. 

In the acquisition step, when the gain is set to auto read, it will read the current gain settings of my Listen hardware. Since it is set to 0dB, it reads that value in and automatically accounts for it.

You can set the gain to specific values, or we can use auto range.

I just set this to Auto range. First it looks at FSD value. If it’s below 0dB FSD and there is available gain to be added, the audio interface will calculate how much gain to add without going over 0dB FSD. It will then automatically add gain and re-run the acquisition step to capture the signal at the new gain stage. If the max FSD is  above 0 dB, the audio interface will automatically remove gain and re-run the acquisition step. 

When I run this sequence, it acquires the data once. It sees that I’m below -30 and adds in 30 dB of gain. Now it runs the acquisition again with that new gain added. And now you can see here the new FSD value on my max FSD in is -5dB which is perfect for making measurements. And if I now look in my AmpConnect settings, we can see it’s changed the gain to plus 30 dB on input 1. This autoranging feature is unique to Listen hardware, and ensures that your input gain is always optimized. It’s included in all current Listen branded hardware products.