What is loudness discomfort levels (LDL)?
The loudness discomfort level (LDL) is the level (intensity of sound) at which a patient reports sound to be uncomfortably loud.
Loudness discomfort levels (LDL) may also be called uncomfortable loudness levels (UCLs) or threshold of discomfort (TDs).
It should be noted that the loudness discomfort levels are variable between individuals, with a normal variation of about 20 dB. This means that one person may have a LDL of 90dB and another may have a LDL of 110dB at the same frequency.
People with hearing loss may also have reduced loudness discomfort levels because hearing loss changes our psychoacoustic perceptions of sound. This is called loudness recruitment.
How are loudness discomfort levels used?
Loudness discomfort levels may be measured during a hearing evaluation, although it is not as common of a practice as it used to be. They are measured at different frequencies, usually 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz using either pulsed tones or narrow band noise. LDLs may also be measured for speech stimuli.
Loudness discomfort levels are used by hearing healthcare professionals when fitting hearing aids. The LDL must be measured to determine the patient's dynamic range of hearing, which is the range of intensities from the softest sound the patient can hear to the loudest sound they can tolerate.
The purpose of determining the patient's dynamic range is the ensure that the hearing aid amplification remains within the comfortable levels of the listener. If LDLs are not measured, an average LDL is used.
Loudness discomfort levels are also commonly measured during a tinnitus evaluation or if hyperacusis is suspected. Reduced loudness discomfort levels is an indication of hyperacusis, and classification of the severity of hyperacusis can be determined based on the LDLs. For example, LDL levels of 95 dB or greater are considered normal. LDLs between 80-90 dB can be considered mild hyperacusis or sound sensitivity, whereas LDLs below 60 dB is considered severe hyperacusis.
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Methods for Measuring Loudness Discomfort Levels
There are two widely accepted ways to measure LDLs.
The most popular is using the Cox Contour Test loudness descriptors. In this method, the patient is presented with a frequency-specific tone or noise stimuli and asked to rate the loudness, as the stimuli volume is slowly increased.
The Cox loudness categories are:
7. Uncomfortably loud
6. Loud, but o.k.
5. Comfortable, but slightly loud
3. Comfortable, but slightly soft
1. Very soft
Once the patient indicates that the sound has reached #7, uncomfortably loud, the volume is not increased and that dB value is graphed on the audiogram.
The second method for measuring loudness discomfort levels is to present the stimuli in ascending intensity and asking the patient to press the button or say “stop” when the sound reaches an uncomfortably loud volume.