Determining the DB level on record and playback ?

Hi, not sure if this is the right section for my questions.

I am not into sound/music, so dumb on all this
my objective really is being able to record, play and analyze in while designing a exhaust system for my racecar is to be able to see while recording and in playback exacting what the sound DB level is to assure sound level is within legal limits and as making exhaust design changes to see by using this software if the design changes made the exhaust sound to loud or not.

I replayed one audio recording I did of the exhaust sound using a single microphone.
I found one function that shows DB but it is in negative values
Does a -12 mean a 88 DB level ?

How can I see the DB level when recording and then in replay ( like a spectrum reading where I do not screw something up and cause it to show a DB level that was not native to when recording ?

JR - Team ZR-1 Corvette Racer’s

dB’s are not an absolute measurement, it is a ratio compared to a standardised level.
In the case of Audacity, 0dB is “full scale” (+1.0 to -1.0 on the vertical scale of the track). All signals recorded in Audacity are with reference to 0dB, and are therefore negative. Silence is “minus infinite dB”.

When talking about “Sound Pressure Levels” (SPL) the reference is often taken as 1 watt at 1 meter distance in free space (no echos). How “loud” this is on your recording will depend on the sensitivity of your microphone, the gain (amplification) of the microphone pre-amp, the distance of the microphone from the sound source, and many other factors - there is no direct correlation between the SPL level and the level shown in Audacity.

As well as all of this there are different “weightings” that can be used when measuring SPL. This is because “how loud” something sounds is frequency dependant. Middle frequencies (around 1kHz) sound much louder than sounds at low or high frequency that have the same power. The “weighting” takes this into account when calculating the SPL. Commonly used weightings are “A weighting” and “C weighting”,

To measure SPL, you need to use an SPL meter. When used according to the instructions these will give a direct readout of sound pressure level and can usually be set to various weighting specifications.

Formula 1 racing cars are limited to 140 something dB (unless it has been reduced in recent years), which is around the pain threshold level for unprotected hearing. Your SPL meter will need to be able to measure SPLs greater than this, and also support the weighting as set down in the specification to which you are working.

Thanks for the feedback

I understand this is not pure fact of the sound level but if I use the same microphone at same distance, same laptop, this software and make exhaust design changes then each test is treated pretty well the same way and should give some aprox DB reading

To understand - a negative zero is no sound and high negative is a louder sound ?

Exporting the plot spectrum in program I see extremes of

Freq (Hz) Level (dB)
21447 -146
172 -12

Does that mean max sound was 146 DB ?
Again I know it is not exact but at least some points to use to see if changes to design causes a DB level for here in USA max DB allowed is 96 DB.

Is this workable for determining aprox DB levels ?


You can’t do what you want with pieces and tools you assembled. The only way to get accurate dB-SPL is with a meter designed to do that. Both of these work very nicely.

Forget the digital one. Digital meters don’t work well on sound because there’s no way to show rapid change in volume. That’s whey they still make the analog one.

There are a number of Hollywood movie theaters set up with these things.

There’s the A Curve and C Curve thing, too. One is absolute sound level and the other is “how your ear works.” The safety laws are written, I believe, in “A.” Most entertainment microphones work in “C.” The meters do both.


Thanks for the info

What about this analog one, it is 40% cheaper then the radio shack one


That looks like a repackage job of the original Radio Shack model. It’s like the one I have – minus the aircraft yellow plastic bits.

How important is the reading? Are you going to start arguing with an OSHA official? Then I wouldn’t be using a cheap knockoff.

The Radio Shack meter is already a cheap knockoff of one of these…

So you’d be buying a bad copy of a cheap knockoff. If you’re that short of bux, see if you can find one on eBay.


I bought the digital model at radio shack as they did not have an analog one and also Northern tool did not have one in stock.

Using the tool inside car with windows up read 105 to 113 DB and if measuring at front side or rear wheels ( about where exhaust tips end was 118 to 124 Db, so way too loud for street or even most tracks max allowed is 96 DB.

I was able to record sound using Audacity then direct the replay to the input of a software program that is a spectrum analyzer and see then a window range of the sound level where the DB meter is one instant of time

What DB level is considered safe, ie not the max of 140 but where ears are not damaged ?


It’s not A Number. It’s sliding scale. 100dBSPL for fifteen minutes is considered one limit.

Scroll down for the chart.


Very good information
Looks like I want to reduce the exhaust design to at least down to 90-95 DB range to maintain engine performance yet safe on ears with helmet when racing or less drive time without one.