Dynamic Productions: Color Mastering Calibrations

HOME CINEMA
ABSOLUTE PLAYBACK dBSPL & HEARING CONSERVATION

Allow me to introduce myself! My name is Marc Davis, full-time I have been practicing medicine since 1997, Critical Care and Nephrology. Part-time, I’ve been professionally calibrating home theaters since 1998, I am ISF & HAA certified. Over the years, I have read many professional white papers, articles, and threads dedicated to the topic of audio calibration. What should the goal dBSPL for main speakers and subwoofers be, is there a ‘reference?’ Once the home cinema is calibrated, what should the absolute playback dB-SPL be? Finally, what is considered a ‘safe’ dB-SPL with respect to hearing conservation? What does the ‘National Institute for Occupational safety and Health’ (NIOSH) have to say with respect to hearing safety and conservation? The goal should be that of experiencing the full dynamic range intended by the audio engineers while avoiding a temporary shift of one’s auditory threshold and/or permanent damage to ones hearing.

Many home theater enthusiasts understand that their audio and video needs calibration so that the art of sight and sound, as intended by the filmmaker may be accurately reproduced in the home. For the purposes of this article I will only touch upon the topic of audio calibration, not video. That being said, I will only be discussing the calibration of speaker levels. I will not be discussing speaker size settings, bass management, setting speaker distance and/or EQ calibration, nor will I be touching on home cinema acoustic treatments.

What defines ‘reference?’ All home theater measurements related to calibration should be taken utilizing ‘C-weighting.’ The master volume should be set to 0dB-SPL (full-scale reference), then, one should utilize the speaker trims to set the dB-SPL for each speaker, individually. When would one calibrate each main speaker to 85dB(C) Vs 75dB(C)?

The main speakers of your home cinema would be calibrated to 85dB(C) and your subwoofers to 95dB(C) when utilizing external narrow-band pink-noise at (-)20dB(C) relative to full-scale, which is 0dB-SPL on your receiver. This allows for 20dB-SPL of head-room, meaning, the main speaker peaks will be 85 + 20 = 105dB(C) peaks/main speaker, and, the subwoofer peaks will be 95 + 20 = 115dB(C) peaks/subwoofer when the master volume is set to 0dB-SPL for playback.

Where then did the 75dB(C) goal for speaker calibration in the home cinema come from? In order to answer this question, one must know whether or not their narrow-band pink-noise is (-)20dB(C) or (-)30dB(C) relative to full-scale. Most home cinema receivers output test tones (narrow-band pink-noise) at (-)30dB(C) relative to full-scale. In this case, one would calibrate to 75dB(C) for the main speakers, and, 75dB(C) for each subwoofer. Wait, wouldn’t I calibrate each subwoofer 10dB greater than the main speakers, just like I do when utilizing external narrow-band pink-noise that is (-)20dB(C) relative to full-scale? No, most receivers boost the LFE signal by 10dB(C) internally, therefore, the main speakers and subwoofers would be calibrated to 75dB(C) utilizing the internal test-tone which is (-)30dB(C) relative to full-scale. The final result, the main speaker peaks will be 75 + 30 = 105dB(C) peaks/main speaker, and, the subwoofer peaks will be 75 + 30 + 10 (internal receiver boost to the LFE signal) = 115dB(C) peaks/subwoofer when the master volume is set to 0dB-SPL for playback. The final results are, in the end, the same as when calibrating to 85dB(C) when utilizing external pink-noise that is (-)20dB(C) relative to full-scale.

Assuming that the speaker sizes, bass management, speaker distances, and EQ were properly set up, as well as the home cinema space being properly treated with acoustic paneling, bass traps, etc., once the dB-SPL of each speaker has been dialed in, you are set, or, are you? From a calibration standpoint you are good to go. However, should you be listening to films at reference, with 105dB(C) peaks/main speaker and 115dB(C) peaks/subwoofer, which is 0dB-SPL on the receiver? If five main speakers and two subwoofers were playing at peak levels (105dB(C)/main speaker and 115dB(C)/subwoofer) simultaneously, the total dB is 118.978dB(C).

The A-scale, or, ‘A-weighting,’ which approximates the ear’s response to moderate-level sounds, is commonly used in measuring noise to evaluate its effect on humans and has been incorporated in many occupational noise standards. The National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) for occupational noise exposure is 85 decibels, A-weighted, as an 8-hr time-weighted average (85 dB(A) as an 8-hr TWA). Exposures at and above this level are considered hazardous to ones hearing. In accordance with NIOSH, the REL for an 8-hr work shift is a TWA of 85 dB(A) using a 3-decibel (dB) exchange rate. When the daily noise exposure consists of periods of different noise levels, the daily dose (D) shall not equal or exceed 100%. The daily dose can be converted into an 8-hr TWA. For example, 79.8dB(A) as an 8-hr TWA is equivalent to a dose of 30% and vice-versa.

Noise-Induced Hearing Loss (NIHL) is caused by exposure to sound levels or durations that damage the hair cells of the cochlea. Initially, the noise exposure may cause a temporary threshold shift - that is, a decrease in hearing sensitivity that typically returns to its former level within a few minutes to a few hours. Repeated exposures lead to a permanent threshold shift, which is an irreversible sensorineural hearing loss.

Hearing loss has causes other than occupational noise exposure. Hearing loss caused by exposure to nonoccupational noise is collectively called sociocusis. It includes recreational and environmental noises (e.g., movies, loud music, guns, power tools, and household appliances) that affect the ear the same as occupational noise. Combined exposures to noise and certain physical or chemical agents (e.g., vibration, organic solvents, carbon monoxide, ototoxic drugs, and certain metals) appear to have synergistic effects on hearing loss [Hamernik and Henderson 1976; Brown et al. 1978; Gannon et al. 1979; Brown et al. 1980; Hamernik et al. 1980; Pryor et al. 1983; Rebert et al. 1983; Humes 1984; Boettcher et al. 1987; Young et al. 1987; Byrne et al. 1988; Fechter et al. 1988; Johnson et al. 1988; Morata et al. 1993; Franks and Morata 1996]. Some sensorineural hearing loss occurs naturally because of aging; this loss is called presbycusis. Conductive hearing losses, as opposed to sensorineural hearing losses, are usually traceable to diseases of the outer and middle ear.

The effects of sound on a person depend on three physical characteristics of sound: amplitude, frequency, and duration. Sound pressure level (SPL), expressed in decibels, is a measure of the amplitude of the pressure change that produces sound. This amplitude is perceived by the listener as loudness. In sound-measuring instruments, weighting networks are used to modify the SPL. Exposure limits are commonly measured in dB(A). When used without a weighted network suffix, the expression should be dB-SPL.

The frequency of a sound, expressed in Hz, represents the number of cycles occurring in 1 sec and determines the pitch perceived by the listener. Humans with normal hearing can hear a frequency range of about 20 Hz to 20 kilohertz (kHz). Exposures to frequency ranges that are considered infrasonic (below 20 Hz), upper sonic (10 to 20 kHz), and ultrasonic (above 20 kHz) are not addressed in this document.

Although no uniformly standard definitions exist, noise exposure durations can be broadly classified as continuous-type or impulsive. All nonimpulsive noises (i.e., continuous, varying, and intermittent) are collectively referred to as “continuous-type noise.” Impact and impulse noises are collectively referred to as “impulsive noise.” Impulsive noise is distinguished from continuous-type noise by a steep rise in the sound level to a high peak followed by a rapid decay. In many workplaces, the exposures are often a mixture of continuous-type and impulsive sounds.

Because NIOSH is recommending a 3dB exchange rate with an 85dB(A) REL, a ceiling limit for continuous-type noise is unnecessary. For example, with an 85dB(A) REL and a 3dB-SPL exchange rate, an exposure duration of less than 28 sec would be allowed at a 115dB(A) level.

The generally accepted ceiling limit of 140dB(A) peak SPL for impulsive noise is based on a report by Kryter et al. [1966]. Ward [1986] indicated that “this number was little more than a guess when it was first proposed.” To date, a proposal for a different limit has not been supported. Henderson et al. [1991] indicated that the critical level for chinchillas is between 119 and 125dB-SPL; and if a 20dB-SPL adjustment is used to account for the difference in susceptibility between chinchillas and humans, the critical level extrapolated for humans would be between 139 and 145dB-SPL. Based on the 85dB(A) REL and the 3dB-SPL exchange rate, the allowable exposure time at 140dB(A) is less than 0.1 sec; thus, 140dB(A) is a reasonable ceiling limit for impulsive noise.

Health effects depend on exposure level and duration. The NIOSH recommendation for a 3dB-SPL exchange rate is based in part on the conclusions from a NIOSH contract report [Suter 1992a]. This report involved an exhaustive analysis of the relationship between hearing loss, noise level, and exposure duration. Although the time/intensity relation ship is most commonly referred to as the exchange rate, it is also referred to as the “doubling rate,” “trading ratio,” and “time-intensity tradeoff.” The 3dB-SPL exchange rate is also known as the equal-energy rule or hypothesis, because a 3dB-SPL increase/decrease represents a doubling or halving of the sound energy. The most commonly used exchange rates incorporate either 3dB-SPL or 5dB-SPL per doubling or halving of exposure duration [Embleton 1994].

The sound level meter is the basic measuring instrument for noise exposures. It consists of a microphone, a frequency selective amplifier, and an indicator. At a minimum, it measures sound level in dB-SPL. An integrating function may be included to automate the calculation of the TWA or the noise dose.

The human ear is not equally responsive to all frequencies; it is most sensitive around 4000 Hz and least sensitive in the low frequencies. The responses of the sound level meter are modified with frequency-weighting networks that represent some responses of the human ear. These empirically derived networks approximate the equal loudness-weighting networks or scales; some also have a B-scale. The A-scale, which approximates the ear’s response to moderate-level sounds, is commonly used in measuring noise to evaluate its effect on humans and has been incorporated in many occupational noise standards.

A sound level meter’s response is generally based on either a FAST or SLOW exponential averaging. FAST corresponds to a 125-millisecond (ms) time constant; SLOW corresponds to a 1-s time constant. The meter dynamics are such that the meter will reach 63% of the final steady-state reading within one time constant. The meter indicator reflects the average SPL measured by the meter during the period selected. In most industrial settings, the meter fluctuates less when measurements are made with the SLOW response compared with the FAST response. A rapidly fluctuating sound generally yields higher maximum SPLs when measured with a FAST response. The choice of meter response depends on the type of noise being measured, the intended use of the measurements, and the specifications of any applicable standard. For typical occupational noise measurements, NIOSH recommends that the meter response on a sound level meter be set at SLOW.

Measuring noise with a sound level meter is relatively simple when the noise levels are continuous and when the worker remains essentially stationary during the work shift. A noise dosimeter is preferred for measuring a worker’s noise exposure when the noise levels are varying or intermittent, when they contain impulsive components, or when the worker moves around frequently during the work shift.

The noise dosimeter may be thought of as a sound level meter with an additional storage and computational function. It measures and stores the sound levels during an exposure period and computes the readout as the percent dose or TWA. Many dosimeters available today can provide an output in dose or TWA using various exchange rates (e.g., 3, 4, and 5dB), 8-hr criterion levels {e.g., 80, 84, 85, and 90dB(A)}, and sound measurement ranges {(e.g., 80 to 130dB(A)}. The choice of FAST or SLOW meter response on the dosimeter does not affect the computed noise dose or TWA when the 3dB exchange rate is used, but it will when other exchange rates are used [Earshen 1986].

NIOSH requires that, for the purposes of hearing conservation, all sound levels from 80 to 140dB(A) be included in the noise measurements. To measure all sound levels from 80 to 140dB(A), a noise dosimeter should have an operating range of at least 63dB-SPL and a pulse range of the same magnitude. In contrast, the ANSI S1.25-1991 standard specifies that dosimeters should have an operating range of at least 50dB-SPL and a pulse range of at least 53dB-SPL [ANSI 1991a]. Today, noise dosimeters with operating and pulse ranges in excess of 65dB-SPL are quite common. Therefore, NIOSH considers that measuring all sound levels from 80 to 140dB(A) with a noise dosimeter is technically feasible.

What does all of this mean for your home cinema experience and hearing conservation, safety? The playback of your favorite film at ‘reference’ dBSPL can be an explosive good time, however, over time, ones ability to hear may suffer. Hearing loss will not only have an effect on ones daily life, it will also imped ones ability to enjoy listening to films.

Listening to films at ‘reference,’ for some, may be uncomfortable, even painful during louder segments of a film. If your ears hurt, ‘listen’ to your bodies warning signal, turn the volume down. If ‘reference’ is 0dB on the receiver, a good rule of thumb is to listen to films 10dBSPL below ‘reference,’ (-)10dB on the receiver.

One must consider the noise dose percentage, measured utilizing a ‘Criterion Level’ of 85dB(A), with a ‘Threshold’ of 80dB(A), and an ‘Exchange Rate’ of 3dBSPL for each film to assess the risk of NIHL. Once the noise dosage for a film is obtained, that percent must be added to the noise dose exposure for the remainder of the day. Should the total noise dose reach 50%, the listener must consider hearing protection, or simply turning that film down to lower the total noise dose and minimize the risk of NIHL.

Each and every home cinema will yield different dosimeter results due to the acoustic properties of the room and perhaps varying calibration methods and/or errors. Faber Acoustical, LLC specializes in developing intuitive software applications (apps) for performing real-time signal analysis, measurement, and data acquisition. Combining their software on Apple's desktop and mobile platforms with a high-quality audio recording interface allows anyone to make efficient measurements of audio band signals with ease and precision. ‘SoundMeter Basic 2018’ by Fabre Acoustical is free and includes an ‘SPL Meter’ as well as a ‘Dosimeter.’ I suggest coupling the app with the MiniDSP UMIK-1 and setting the UMIK-1 internal dip-switches to a 0dB Gain to ensure accurate measurements and avoid clipping. Fabre Acoustical apps support the MiniDSP and one can upload the calibration file specific to ones mic using the serial number provided with the MiniDSP. However, the UMIK-1 MUST BE MANUALLY CALIBRATED for accurate results! I have found the factory calibration file to be unreliable for the MiniDSP microphones. I suggest purchasing the ‘Galaxy Audio CM-200’ to calibrate the MiniDSP UMIK-1 to 114dB(C) @ 1kHz.

I have begun to measure films at 10dBSPL below reference, (-)10dB on the receiver. Below you will find the results for ‘The Lord of the Rings: Fellowship of the Ring’ (Theatrical) and ‘The Hobbit: An Unexpected Journey’ (Extended), as well as a glossary of terms. I truly hope this article was both informative and enjoyable. Be mindful of your hearing, preserve your ability to enjoy listening to films over a lifetime and avoid ‘Noise Induced Hearing Loss’ (NIHL) - Sincerely and most respectfully, Marc Davis.

Dosimeter Samples

The Lord of the Rings: Fellowship of the Ring
Peak dBSPL = 111.40dB(A)
Equivalent Level: 84.20dB(A)
Noise Dose: 29.31%
TWA: 79.69dB(A)

The Hobbit: An Unexpected Journey
Peak dBSPL = 111.82dB(A)
Equivalent Level = 82.54dB(A)
Noise Dose = 19.51%
TWA = 77.93dB(A)

Glossary

Peak: The maximum value reached by the sound pressure, there is no time constant or time weighting applied. This is the true peak of the sound pressure wave.

Equivalent Level: Average dBSPL over the total duration of time measurements were taken.

Noise Dose: Noise dose, is the amount of noise as a percentage normalized to an 8-hour work-day. Exposures at 100% or above are considered hazardous.

TWA: Time weighted average is the total sound level over a period of time, normalized to an 8-hour work-day.

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🔊THX REFERENCE LEVEL EXPLAINED 🔊

What is ‘THX Reference Level’?

Reference level is a calibrated volume setting used for both movie production (in dubbing stages and post production houses) and reproduction (in screening rooms and theaters). The human hearing system is non-linear, especially in the bass, so having a consistent playback level – a reference – is critical if the mix is to translate from one production house to another and audiences are to hear the director’s intent in terms of the balance in the soundtrack between dialog, effects and ambiance.

Reference level for all channels except low frequency effects is calibrated by adjusting the audio chain such that a pink noise signal recorded at -20dB relative to full scale (0dB) creates 85dB sound pressure level as measured with a C weighted SPL meter at the seating locations. Volume levels are adjusted for each channel individually until they read 85dB. The master volume control setting associated with this playback level is then set to a nominal 0dB, or reference level. The history behind this is that sound engineers and producers generally work so that the average recording level for dialog in movie soundtrack is -20dB. This allows for 20dB of dynamic range in the soundtrack. The low frequency effects channel is calibrated higher, so that a -20dB signal reaches 95dBC at the seating locations.

What does ‘Reference Level’ mean for home theater design?

Reference level means two things for home theater design:

1. Speakers and amplifiers must be capable of 105dB peaks

If the playback chain is calibrated to produce 85dB for a -20dB signal at the listening position then the speakers and amplifiers could be asked to produce 105dB for a 0dB signal. It is a challenging proposition for an audio system to reproduce this level cleanly, without dynamic compression and to be able to do so reliably. Most standard consumer technologies such as soft dome tweeters are not up to scratch in any reasonably sized room. Speakers should have high sensitivity and high power handling, such as the Procella Audio speakers we recommend and use.

2. Subwoofers must be capable of 115dB peaks

The low frequency effects channel is handled slightly differently and has a 10dB boost relative to the other channels. The maximum SPL that subwoofers could be asked to reproduce from the low frequency effects track is therefore 115dB at the listening position. In reality the situation is nearly always worse because the subwoofer must additionally reproduce bass managed* content from other channels. These challenges mean that multiple large subwoofers are typically needed to be able to properly reproduce the soundtrack as the director intended.

* Bass managed content is that from other speaker channels that has been diverted to the subwoofer. In home audio video receivers (AVRs) and pre-processors this is done by setting the speakers to small in the bass management menu and specifying a crossover frequency. With surround speakers, for example, an 80Hz crossover is typically used. This means that any content in the surround channels under 80Hz is essentially diverted to the subwoofer. For 5 bass managed speakers an additional 6dB and for 7 bass managed speakers an additional 8dB of output may be required from the subwoofer channel.

The smallest shift in color during a movie can vastly affect its mood or atmosphere - but who adjusts this behind the scenes and why?

Welcome to 'Color Matters', a four-part miniseries by Portrait Displays. Episode one dives into the philosophy and vision of FotoKem Hollywood colorist, Alastor Arnold, and FotoKem color scientist, Joseph Slomka, as they give you an inside look behind the post-production process and how they use the power of color to produce beautiful, dynamic works.

COLOR MATTERS | Episode 1 - 'Philosophy & Vision' The smallest shift in color during a movie can vastly affect its mood or atmosphere - but who adjusts this behind the scenes and why? Welcome to 'Color Matte...

🎞 DYNAMIC PRODUCTIONS - C.M.C. 🎞

New OLED for the holidays? Your LG OLED is capable of being professionally calibrated to the same standard utilized by post-production movie houses. Watch your material and see it exactly as it was intended to look by the director. Calibration improves shadow detail, colors are displayed correctly, and the image will have 3D like depth. Also, calibration will extend the life of your OLED! Phosphors will no longer be overdriven and will be capable of delivering an astoundingly accurate image for years to come.

Using the top calibration software - CalMAN, I’m able to calibrate the internal LUT (look up table), leaving the user settings at default. This allows for fine tuning that’s not possible via the user controls. LG has worked tirelessly with Portrait Displays, the maker of the CalMAN software, to ensure impeccable calibration integration. The consumer LG OLED is used in post-production movie houses as a home reference monitor for the colorist. Watch material exactly as the finished film was intended to look.

My colorimeter and spectroradiometer are the finest in the business. In fact, I utilize the same calibration meters used to calibrate post-production monitors in the colorist suites of Hollywood. The Colorimetry Research CR-100 & CR-250-RH ensure that all readings are profoundly accurate, meeting and exceeding the standards for image quality.

Calibration will bring your LG OLED to life, unlocking the full potential that the best panel on the market has to offer. Enjoying a STAR WARS marathon or playing HALO INFINITE and finishing the fight, your calibrated LG OLED will deliver in a way you never thought possible.

Email me today for a free quote and holiday specials!

🎭 ‘Marc Davis’ in Orlando, Florida at Email:

[email protected]

🦁 HAPPY FATHER’S DAY 🦁

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