Volume and level controls are among the most used in audio playback systems. The proper listening volume varies wildly depending on the set and setting. For example, a rock concert will be much louder than a guided sleep meditation. Understanding listening levels is important for whatever we choose to listen to. What volume should audio be listened to and mixed at? Critical listening should be done at various levels, though 80 - 85 dB SPL is the sweet spot with the best frequency balance and low risk of hearing damage. Low levels help us identify elements too low in the mix, while high levels let us hear/feel the mix at a higher risk of hearing damage. In this article, we'll discuss how the human auditory system responds to different listening levels, what constitutes safe listening levels, and how we should take advantage of different listening levels when listening critically to music and audio. Though this article has been written in a way that primarily addresses mixing engineers, everyone interested in music and audio will benefit from reading it. Understanding Sound Pressure Level In order to work with real-world numbers rather than subjectivity, we must first understand sound pressure level. With this objective measurement, we can move forward with our discussion on loudness and listening level with a mutually agreed-upon scale. Let's begin with sound pressure (technically different than sound pressure level). Sound pressure is the deviation from ambient pressure in a medium caused by a sound wave. Sound waves are longitudinal waves, meaning that the vibration of the medium (gas, liquid or solid) is parallel to the direction in which the wave travels. Displacement of the medium, which causes deviation in pressure, happens in the same and opposite direction of the wave propagation. Sound pressure is measured at a single point (at a microphone, a hydrophone, an ear, etc.). Sound waves lose energy as they travel through a medium. Energy is lost as heat due to the friction between the molecules of the medium that get displaced by the sound wave. Sound waves also reflect off surfaces, and there are often multiple sound sources in any given environment. Various sound waves will interact to produce certain sound pressure values at a given location within an environment. These complex factors all play into the SPL at any given location and time. The SI unit Pascal (Pa) is the standard unit to measure sound pressure is the SI unit Pascal (Pa). 1 Pa = 1 kg / m • s2 Sound pressure level (SPL) is a logarithmic measure of sound pressure relative to a reference value at the threshold of hearing. SPL is nearly always measured in dB SPL or "decibels relative to the sound pressure threshold of human hearing at 1,000 Hz." The sound pressure threshold of human hearing for a 1,000 Hz tone is universally accepted as 2 x 10-5 Pa or 0.0002 Pa. That means that an rms (root mean square) or "average" variation of 2 x 10-5 Pa about the ambient pressure can be heard by humans, assuming the sound is a 1,000 Hz sine wave. This 1 kHz tone is an important piece of the measurement. Our ears are not perfectly balanced within the universally-accepted audible range of 20 Hz to 20 kHz. We're more sensitive to certain frequencies than others, and, on top of that, our sensitivity changes at different sound pressure levels. To illustrate this natural "frequency response", we can turn to the Fletcher-Munson curves (published in 1933) and the equal-loudness level contours (published in 1955). Both show how we hear frequencies differently: Source: https://commons.wikimedia.org/wiki/File:Lindos4.svg Here we have frequency on the x-axis and sound pressure level on the y-axis. The lines represent phon, a logarithmic unit of loudness level for tones and complex sounds. We can see a region in the 2 - 6 kHz range where we will hear sound well below the 0 dB SPL "threshold of hearing". Conversely, we will need much more sound pressure (above 0 dB SPL) to hear the lower and high frequencies. The relative imbalances between frequencies begin leveling out as sound pressure levels increase. This is important information to know, and we'll touch on the human auditory response in later sections of this article. For now, we have the following equation: dB SPL value = 20 • log10 (P / P0) Where:P is the sound pressure (in Pascals)P0 is the reference point of 2 x 10-5 Pa or 0.0002 Pa This logarithmic scale is useful because we perceive a doubling in loudness as a 10 dB SPL increase. It's easier to envision a 10 dB increase as a doubling of perceived loudness than relying on Pascal values. In the following table, we have dB SPL ratings along with their respective pressure measurements (in Pascals). Common examples of sources that produce these sound levels are also shown. dB SPLPascalSound Source Example 0 dB SPL0.00002 PaThreshold of hearing 10 dB SPL0.000063 PaLeaves rustling in the distance 20 dB SPL0.0002 PaBackground of a soundproof studio 30 dB SPL0.00063 PaQuiet bedroom at night 40 dB SPL0.002 PaQuiet library 50 dB SPL0.0063 PaAverage household with no talking 60 dB SPL0.02 PaNormal conversational level (1 meter distance) 70 dB SPL0.063 PaVacuum cleaner (1 meter distance) 80 dB SPL0.2 PaAverage city traffic 90 dB SPL0.63 PaTransport truck (10 meters) 100 dB SPL2 PaJackhammer 110 dB SPL6.3 PaThreshold of discomfort 120 dB SPL20 PaAmbulance siren 130 dB SPL63 PaJet engine taking off 140 dB SPL200 PaThreshold of pain The varying sound pressure is generally referred to in a root-mean-square fashion rather than peak-to-peak. Root mean square (rms) is a measurement of the "average" SPL. Technically, averaging doesn't work in the case of sound pressure because it produces both positive and negative pressures relative to the ambient pressure of the medium. I dive deeper into the complexities of decibels in my article What Are Decibels? The Ultimate dB Guide For Audio & Sound. You Should Ideally Mix/Listen Critically At All Practical Levels When it comes to mixing, it's worthwhile to listen at all practical levels. By practical levels, I mean loud enough to be heard but quiet enough that it doesn't immediately damage your hearing. It's important to know what the mix will sound like at as many different levels as possible. Do your best to make it sound great at every listening level. 85 dB SPL can be quite loud, but it's a level that we can listen to for extended periods of time (a full rok day) without risking hearing damage. Any louder than 85 dB SPL and our exposure time before hearing damage is reduced. The louder we choose to monitor our mixes, the less time we have before sustaining noise-induced hearing damage. At 85 dB SPL, the natural frequency response of our auditory system is relatively flat, allowing us to hear the low-end and high-end more clearly. This is shown in the graphs mentioned earlier in this article. Mixing and listening at higher levels will undoubtedly give more impact and will arguably sound even better. However, levels above 85 dB SPL shouldn't be maintained over long mixing sessions and ought to be only be used periodically to hear what the mix sounds like loud. Mixing at lower levels will focus our ears on the mid-range, which make up the frequencies that most of the mixing decisions will affect. Opting to mix at lower levels can give us the benefit of mixing everything nicely so that we can hear each element appropriately within the mid-range. This can be especially beneficial for bass elements, which may get mixed too low if we're mixing at higher levels (where the low-end is relatively loud). Because the mid-range is so important, it's much more likely that a song mixed at high levels will fall apart at low playback levels than a song mixed at low levels falling apart at high playback levels. You may be able to get away with louder levels in larger and better-treated rooms. 85 dB SPL in a large room can be an ideal listening level, where the hearing response is relatively flat and the exposure time before hearing damage is long. However, 85 dB SPL may be too loud in smaller rooms when the reflections are summed together. However, as a good rule of thumb, we should opt to mix at a level where we can maintain a conversation over the music without having to shout. With normal conversational levels hovering around 60 dB SPL, we can choose to monitor around this level. If you're into mixing, be sure to check out my article Essential Processors/Processes For Mixing Music & Audio. It's advisable to find a good, low listening level to do the majority of your mixing at. One that you can listen to for an extended period of time. By having your own calibrated listening level, you'll train yourself to become proficient at mixing with whatever the natural frequency response of your auditory system is at that level. Taking regular breaks can help reduce ear fatigue, especially at higher monitoring levels. These breaks are essential in allowing us to ultimately mix longer and maintain our objectivity without sustaining hearing damage. Furthermore, changing up the monitoring levels periodically is a useful practice for being able to hear the mix differently. It's arguably as important as other monitor-switching practices, including summing to mono, bandpass filtering the lows and highs, switching between monitor pairs, checking in headphones, etc. I have a video where I talk more about the benefit of monitoring at different levels. Check it out here: https://youtu.be/Y4Rd9HJF3Zs If you want to produce louder mixes, be sure to check out My New Microphone's Top 12 Professional Tips To Make Audio Mixes Louder. Listening For Enjoyment When listening for enjoyment rather than critique, listen at whatever level feels good but realize the dangers of turning the music up too loud. As was suggested earlier, anything above 85 dB for an extended period can cause hearing damage. Be aware of your exposure time to loud music. Pay special care if you listen through earbuds or earphones that fit directly into the ear canal. Related article: Should I Buy Earbuds Or Headphones? (In-Depth Comparison) Consider hearing protection when going to concerts to help bring down the SPL at your ears. Related article: Top 11 Best Earplug Brands For Live Music & Jams/Rehearsals Take frequent breaks from listening to loud music when possible. With these general safety tips covered, let's move on to more objective data to help protect our hearing. NIOSH And OSHA The follow-up question then becomes about safety. We know that we can't listen to very loud sources for very long without sustaining hearing damage. So for health and safety reasons, how long is considered too long, and for which sound pressure levels? We'll visit two main standards in this article: the NIOSH and OSHA. The NIOSH (National Institute for Occupational Safety and Health) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. The OSHA (Occupational Safety and Health Administration) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Below are the noise exposure limits as recommended by the NIOSH and OSHA: NIOSH Standard (dBA)Equivalent Sound Pressure Level (at 1 kHz)Maximum Exposure Time LimitOSHA Standard (dBA)Equivalent Sound Pressure Level (at 1 kHz) 127 dBA127 dB SPL 44.8 Pa1 second160 dBA160 dB SPL 2.00 kPa 124 dBA124 dB SPL 31.7 Pa3 seconds155 dBA155 dB SPL 1.12 kPa 121 dBA121 dB SPL 22.4 Pa7 seconds150 dBA150 dB SPL 632 Pa 118 dBA118 dB SPL 12.6 Pa14 seconds145 dBA145 dB SPL 356 Pa 115 dBA115 dB SPL 11.2 Pa28 seconds140 dBA140 dB SPL 200 Pa 112 dBA112 dB SPL 7.96 Pa56 seconds135 dBA135 dB SPL 112 Pa 109 dBA109 dB SPL 5.64 Pa1 minute 52 seconds130 dBA130 dB SPL 63.2 Pa 106 dBA106 dB SPL 3.99 Pa3 minutes 45 seconds125 dBA125 dB SPL 35.6 Pa 103 dBA103 dB SPL 2.83 Pa7 minutes 30 seconds120 dBA120 dB SPL 20.0 Pa 100 dBA100 dB SPL 2.00 Pa15 minutes115 dBA115 dB SPL 11.2 Pa 97 dBA97 dB SPL 1.42 Pa30 minutes110 dBA110 dB SPL 6.32 Pa 94 dBA94 dB SPL 1.00 Pa1 hour105 dBA105 dB SPL 3.56 Pa 91 dBA91 dB SPL 0.71 Pa2 hours100 dBA100 dB SPL 2.00 Pa 88 dBA88 dB SPL 0.50 Pa4 hours95 dBA95 dB SPL 1.12 Pa 85 dBA85 dB SPL 0.36 Pa8 hours90 dBA90 dB SPL 0.63 Pa 82 dBA82 dB SPL 0.25 Pa16 hours85 dBA85 dB SPL 0.36 Pa As we can see, both agencies note sound pressure levels in dBA (decibels A-weighted), which takes into account the variation in hearing sensitivity and perception across the audible range of frequencies. dBA gives us a better representation of what we hear as opposed to dB SPL, which is independent of frequency-specific sensitivities in human hearing. The second thing to note is that there is a significant difference in recommendations between the two agencies. The relatively lenient OSHA recommendations allow for longer exposure times at loud levels. The relatively stringent NIOSH recommendations are more protective of hearing and are based on studies relating noise exposure to hearing loss. Both standards make the following assumptions: Noise levels occur as part of a work environment. The work environment is limited to 8-hour days, 5 days per week, over a 40-year working lifetime. Time away from work is quiet. Using A Decibel Meter Knowing the limitations of our hearing and the safe exposure times for different listening levels is great. However, we can't make safe choices if we aren't aware of the sound pressure level we're exposed to. I laid out dB SPL ratings of common sources and environments in an earlier table. However, measuring with a decibel meter is the best way to know how loud your environment is (and, more specifically, your position within the environment). The Galaxy Audio Check Mate CM-130 (link to check the price on Amazon) is a great option that reads accurately between 40 and 130 dB SPL. Galaxy Audio Check Mate CM-130 Related Question Is playing music loud bad for speakers? Playing music/audio too loud may cause damage to speakers due to excess heat in the drivers or even mechanical failure of the driver suspension. Speakers have power ratings that, when exceeded (by increasing the amplifier/volume control), will burn/melt the driver coil and damage the speaker. Related article: Is Playing Music Loud Bad For (Damaging To) Speakers? What does a maximum sound pressure level actually mean? The maximum sound pressure level of a microphone is not the pressure level that will destroy the microphone. Rather, max SPL is the sound pressure threshold at which a microphone's output signal begins to distort. Related article: What Does A Microphone's Maximum Sound Pressure Level Actually Mean?
