How to create a 42dBa sine wave

Hi, a brand new user here. Using win10 Pro and Audacity 2.3.2. Can someone clear up my confusion trying to create a sound wave of 42dBa? I’m trying to confirm the calibration of the Decibel app on my iPhone. Thx very much!

When you play a sine wave in Audacity (or any other player), how loud it plays depends on your amplifier and speakers as well as on the size of the sine wave signal. To create a sound wave of 42dBa, you need to generate a sound wave, play it, and adjust your amplifier until the sound is 42 dBA.
In short, to calibrate your app, you need a Sound Pressure Level meter (SPL meter) that is already calibrated.

You’ll need a calibrated SPL meter. iPhones should be fairly consistent and there are a limited number of models so hopefully the app developer has done a good job and it should be fairly accurate. I wouldn’t trust a similar app for an Android unless it has settings for your particular phone.

You can generate a sine wave at a known digital level (dBFS = Decibels full scale, where 0dB is the “digital maximum”) but the acoustic dB SPL level depends on your volume control setting, the gain or your amplifier, the sensitivity/efficiency of your speakers, how far you are from your speakers, and room acoustics if you’re indoors (and maybe other factors I forgot to mention).

dBFS levels are normally negative. The 0dB SPL reference is approximately the threshold of human hearing so dB SPL readings (such as 42dB SPL A-weighted) are positive. But, the number ARE CORELLATED and they CAN be calibrated. If you have a digital level of -10dBFS and that plays-back at 42dB SPL and you reduce the digital level to -12dBFS, you’ll have -40dB SPL, etc.

To check your sound level meter, start with a sound level meter.

Radio Shack had multiple versions right up to the end.

I can usually come up with a shortcut using commonly available tools or parts—such as creating white noise by crushing a newspaper page—but I can’t with this one.


I’m trying to confirm the calibration of the Decibel app on my iPhone.

There is one oddball thing you can do. Compare two iPhones. If they’re wildly different then the whole premise is rubbish.


Nobody ever esquires about sound pressure meters unless they are trying to prove their workplace is too loud, or if it isn’t.

Are you one of these people?


Thx to everyone that replied to my question! In reply to the query posed by Kozikowski, my interest did not an office environment but whether a dishwasher was as quiet as the manufacturer claimed.