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How Dynamic Range, Compression, and Headroom Affect Audio

More than just volume control

A lot of money is invested in the sound performance of your home theater or stereo system. Volume control is the primary control people look for, but it has a limited impact on the quality of the listening experience. Headroom, dynamic range, and dynamic compression are additional factors that affect the overall listening experience.

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Headroom: power when you need it

For surround sound, a stereo or home theater receiver must power the speakers. Because sound levels are constantly changing during music recordings and movies, receivers must quickly and constantly adjust output power.

Headroom refers to the ability of a stereo, home theater receiver or amplifier to boost power to a higher level in a short period of time. This is designed to capture musical peaks or extreme sound effects in movies. This is especially important in home theater systems, where extreme volume changes occur during movies.

Headroom is measured in decibels (dB). If a receiver or amplifier can double its continuous output power, it must have a dynamic range of 3 dB. However, doubling the power output doesn’t mean doubling the volume. To double the volume at a point, the receiver or amplifier must increase the output power by a factor of 10.

This means that if a receiver or amp is outputting 10 watts at some point in time, and a sudden change in the track requires twice as much volume in a short period of time, the amp or receiver should be able to quickly output 100 watts.

Headroom is built into the hardware of the receiver or amplifier and cannot be adjusted. Ideally, a home theater receiver has a dynamic range of at least 3 dB or more. This can also be expressed in terms of the maximum output power of the receiver. For example, if the maximum or dynamic output power is twice the specified or measured RMS, continuous or FTC power, this would be an approximation of 3 dB of dynamic range.

Dynamic Range: Soft and High

In audio, dynamic range is the ratio of the loudest, undistorted sound produced to the softest sound that can still be heard. A decibel is the smallest difference in volume that the human ear can perceive. The difference between a whisper and a loud rock concert (same distance from your ears) is about 100 dB.

That means, using the dB scale, a rock concert is 10 billion times louder than a whisper. For recorded music, a standard CD can reproduce a dynamic range of 100 dB, while an LP record has a dynamic range of about 70 dB.

For stereos, home theater receivers and amplifiers, you need something that can produce the dynamic range of a CD or other source. One problem with source content recorded with wide dynamic range is that the “distance” between the softest and loudest parts can be annoying.

For example, in poorly-mixed music, the sound may be drowned out by background instruments, while in a movie, the dialogue may be too soft and incomprehensible, even though the sound effects can be heard on the street.

This is where dynamic compression comes into play.

Dynamic compression: reduce dynamic range

Dynamic compression does not refer to the type of compression format used in digital audio such as MP3. Instead, dynamic compression is a tool that allows listeners to change the ratio between the loudest and softest parts of an audio track when playing a CD, DVD, Blu-ray Disc, or other file format.

For example, if a track’s explosions or other elements are too loud and the dialogue is too soft, you’ll want to reduce the dynamic range in the track. When you do that, the explosions won’t be as loud, but the dialogue will be louder. This results in a smoother overall sound, which is useful when playing CDs, DVDs or Blu-ray discs at low volume.

In a home theater receiver or similar device, the amount of dynamic compression is adjusted by a setting knob, which may be called dynamic compression, dynamic range, or DRC.

Comparable brands of dynamic compression control systems include DTS TruVolume, Dolby Volume, Zvox Accuvoice and Audyssey Dynamic Volume. Some compression or dynamic range options also work with different sources, like changing the channels on your TV so that all channels are at the same volume level, or taming those loud commercials in a TV show.

it boils down to

Headroom, dynamic range, and dynamic compression are important factors that affect the volume range in a listening environment. If adjusting these levels doesn’t solve your problem, consider looking at other factors such as distortion and room acoustics.

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How Dynamic Range, Compression, and Headroom Affect Audio

Beyond mere volume control

A lot goes into sound performance on a stereo or home theater system. The volume control is the main control people reach for, but it can only do so much to affect the quality of a listening experience. Dynamic headroom, dynamic range, and dynamic compression are additional factors that can contribute to the overall listening experience.

MistkaS / Getty Images
Dynamic Headroom: Power When You Need It

For room-filling sound, a stereo or home theater receiver needs to put out a certain about of power to your speakers. Because sound levels constantly change throughout musical recordings and movies, the receiver needs to adjust its power output quickly and in a consistent manner.

Dynamic headroom refers to the ability of a stereo, home theater receiver, or amplifier to blast the power to higher levels for short periods of time. This is meant to accommodate musical peaks or extreme sound effects in films. It is especially important in a home theater system, where extreme volume changes occur throughout the course of a film.

Dynamic headroom is measured in decibels (dB). If a receiver or amplifier has the ability to double its continuous power output capability, it should have 3 dB of dynamic headroom. However, doubling the power output does not mean doubling the volume. In order to double the volume from a given point, a receiver or amplifier needs to increase its power output by a factor of 10.

This means that if a receiver or amplifier is outputting 10 watts at a specific point, and a sudden change in the soundtrack requires double the volume for a brief period of time, the amplifier or receiver needs to be able to rapidly output 100 watts.

Dynamic headroom capability is baked into the hardware of a receiver or amplifier, and it cannot be adjusted. Ideally, a home theater receiver will have at least 3 dB or more of dynamic headroom. This can also be expressed by a receiver’s peak power output rating. For example, if the peak or dynamic power output rating is double the amount of the stated or measured RMS, Continuous, or FTC power rating, this would be an approximation of 3 dB dynamic headroom.

Dynamic Range: Soft vs. Loud

In audio, dynamic range is the ratio of the loudest undistorted sound produced in relation to the softest sound that is still audible. One dB is the smallest volume difference that a human ear can detect. The difference between a whisper and a loud rock concert (at the same distance from your ear) is about 100 dB.

This means that, using the dB scale, the rock concert is 10 billion times louder than the whisper. For recorded music, a standard CD is capable of reproducing 100 dB of dynamic range, while the LP record tops out at about 70 dB.

When it comes to stereos, home theater receivers, and amplifiers, you want something that can produce the dynamic range of a CD or other source. One problem with source content that has been recorded with a wide dynamic range is that the “distance” between the softest and loudest portions can be irritating.

For example, in poorly mixed music, a vocal may appear to be drowned out by the background instruments, and in movies, the dialog may be too soft to understand, even as the sound effects can be heard down the street.

This is where Dynamic Compression comes in.

Dynamic Compression: Squeezing Dynamic Range

Dynamic compression does not refer to the types of compression formats used in digital audio (such as MP3). Instead, dynamic compression is a tool that allows a listener to change the relationship between the loudest and quietest parts of the soundtrack when playing a CD, DVD, Blu-ray Disc, or another file format.

For example, if explosions or other elements of a soundtrack are too loud and the dialog is too soft, you would want to narrow the dynamic range present in the soundtrack. Doing so makes the sounds of the explosions not quite as loud, yet the dialog sounds louder. This makes the overall sound more even, which is useful when playing a CD, DVD, or Blu-ray Disc at low volume.

On home theater receivers or similar devices, the amount of dynamic compression is adjusted using a setting control that may be labeled dynamic compression, dynamic range, or DRC.

Similar brand-name dynamic compression control systems include DTS TruVolume, Dolby Volume, Zvox Accuvoice, and Audyssey Dynamic Volume. In addition, some dynamic range or compression control options can work across different sources, such as when changing channels on a TV so that all the channels are at the same volume level, or taming those loud commercials within a TV program.

The Bottom Line

Dynamic headroom, dynamic range, and dynamic compression are important factors affecting the range of volume in a listening environment. If adjusting these levels doesn’t fix the problems you experience, consider looking into other factors like distortion and room acoustics.

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