I recently purchased some hi-fi earbuds for recreation listening when using my iPhone. While the headphones themselves are great, what I found particularly interesting was a flyer included in the headphones packaging.
The flyer includes a chart that lists the decibel level (dB) of various sound effects. We’ve seen these charts before. This one’s a bit different. I wanted to include this particular chart in a series to consider two important ideas. The first: how does gear affect field recordings you capture?
Sound Clip Decibel Levels
Here’s the chart. I’ve scanned it from the original flyer. Click the image below for a larger version:
That inspired me to make a more detailed chart listing decibel levels for common sound effects. I sourced them from the Web and from Wikipedia:
|Softest sound possible (at 1 kHz)||0|
|Rustling leaves||Specific||10||Barely audible|
|Whispering at 5 feet||Specific||20|
|Soft whisper||Specific||30||Very quiet|
|Very calm room||Ambience||30|
|Quiet office or library||Ambience||40|
|Quiet residential area||Ambience||40|
|Passenger car||Specific||70||Difficulty hearing speech|
|Power lawn mower||Specific||80||Irritating|
|Pop - up toaster||Specific||80|
|Food mixer or food processor||Specific||85|
|Factory machinery||Specific||100||Very loud|
|Baby crying||Specific||110||Extremely loud|
|Busy video arcade||Ambience||110|
|Shouting in ear||Specific||111|
|Football game (stadium)||Ambience||117|
|Hammer hitting nail||Specific||120|
|Jet taking off (60 metres)||Specific||120|
|Air raid siren||Specific||130|
|Stock car race||Ambience||130|
|Loudest possible voice||Specific||135|
|Airplane taking off||Specific||140|
|Jet taking off||Specific||150|
|Artillery fire (500 feet)||Specific||150|
|30-06 rifle being fired||Specific||171|
|Rocket launching (at pad)||Specific||180|
|Sound waves become shock waves||191|
You can view it on Google Sheets, or download a copy from the links below:
Not all distances to the subjects were noted, however, most specifics were within 1 meter.
A Guide to Gear Capabilities
Why are these charts interesting?
First, you can use it as a guide for field recording sound effects. We all know that not all recorders and microphones are created equally. Some are designed to shine when paired with certain sound effects, or when doing specific tasks.
That’s why the chart is intriguing: it shows us what is technically required to capture certain sounds. There are many ways to think about this, but I’ll focus on three:
- Microphone maximum SPL.
- Self noise.
1. Maximum SPL
First, not every microphone can capture loud sounds at all. Some may top out at certain decibel ratings and are unable to capture louder sounds. This measurement is known as maximum sound pressure level (SPL). For example, Audio-Technica’s BP4029 stereo shotgun condenser microphone can handle a maximum of 126 dB (click the “Specifications” tab at the link above). That means jet engines and rifle blasts are beyond the capabilities of that microphone.
What happens when attempting to record sounds higher than a microphone’s max SPL rating? The microphone’s diaphragm will be flattened. It just isn’t sensitive enough to capture the powerful waveforms from loud sounds. The result? The sound will be distorted.
What decibel level can your microphone capture? Read a post listing popular microphone statistics to learn more.
There’s also the idea of bit-depth. Most recorders now provide 24-bit recording. That accommodates for 144.49 dB of signal-to-noise information. What about 16-bit? That tops out at 96.33 dB.
Here’s a chart of other popular bit rates:
|Bit Depth||Signal-to-Noise Ratio (dB)|
How can you improve the dynamic range to capture both quiet and loud sounds? Want the quickest way to expand the number of subjects you can record? Increase your bit depth.
What about quiet sounds? The chart shows us that leaves rustling creeps in at a mere 10 dB. The problem with these sounds isn’t whether or not a microphone can capture 10 decibels. The issue is different: self-noise. This is important when recording soft sounds.
All equipment creates its own noise, referred to as self-noise (or equivalent input noise (EIN)). The very best equipment will create less noise. Less refined gear will introduce more noise into the signal. The result? The noise of the equipment will compete with the quiet sound of the subject.
So, in other words, the list invites us to question how much noise a microphone introduces into a recording. Will this noise be louder than sounds on the list?
Our BP4029 microphone weighs in at 24 dB of self-noise. That means the noise of the equipment will be louder than the rustling leaves (10 dB) it is trying to record. So, considered a certain way, it’s pointless to try to record rustling leaves with this microphone. A recording of a quiet library (40 dB) would be more successful, however the field recording with the BP4029 would still contribute 24 dB of noise to the recording.
Of course, a microphone’s self-noise rating doesn’t tell the whole story of its capabilities. Also, the preamp circuitry’s noise as well as the ambient noise of the location will affect how much noise is in the recording, too. However, considering the noise of the gear and the decibel level of a subject gives field recordists a glimpse into the type of recordings are possible with certain kit.
Decibel Guidelines for Recording
Now, there are other techniques and technologies that allow a field recordist to capture loud sounds typically beyond equipment’s abilities: pads, attenuators, limiters, and so on. There are ways to capture quiet sounds more easily. Also, it’s important to note that specification ratings can be influenced by many factors such as air pressure, frequency, and much more.
However, it’s valuable to look at the raw numbers of subject decibel ratings and equipment stats. Combined, they provide a starting point to learn how the decibel rating of a subject will affect field recording and the equipment used to capture sound fx.
Keep these numbers in mind when choosing gear. A general guideline is that more sophisticated equipment is needed to capture very loud sounds or very quiet ones. Sounds in the middle of our decibel chart are more easily captured. That’s why beginning field recordists find the most success with subjects in the middle of the spectrum. Even the most advanced field recordists struggle to capture sounds at either extreme. But that’s a subject for an upcoming article.
How to Measure Decibel Levels
Of course, not every sound is listed here. Curious how loud the sounds around you are?
You can measure them with a sound level meter, also known as a sound pressure level meter (SPL). This is a device that uses a condenser microphone to measure the changes in air pressure from sound waves. The microphone is typically at the top of the unit, away from the body of the instrument, ensuring more accurate readings. When sound waves cause the air pressure to change, the movement of the microphone’s diaphragm is converted to an electric signal (in volts), and translated into sound pressure levels (decibels dB SPL) which is displayed on a screen of the instrument.
Here are few popular ones on Amazon if you’d like explore purchasing one yourself.
- Want to know which microphones accommodates quiet sounds and loud ones? I wrote an earlier post examining popular microphone specifications. It lists the maximum SPL, self-noise, and other data.