roomCriteria

R2026b

Evaluate room background noise using room criteria (RC) curves

Since R2026b

Syntax

RC = roomCriteria(audioIn,fs)

RC = roomCriteria(Leq)

RC = roomCriteria(___,Name=Value)

[RC,LMF] = roomCriteria(___)

[RC,LMF,QAI] = roomCriteria(___)

[RC,LMF,QAI,rattleRisk] = roomCriteria(___)

roomCriteria(___)

Description

RC = roomCriteria(audioIn,fs) returns the room criteria (RC) level according to the ANSI/ASA S12.2-2019 standard [1]. The function designates an RC curve and a spectrum classification based on the procedure outlined in the standard.

RC = roomCriteria(Leq) computes the RC level using equivalent continuous sound pressure level (SPL) measurements across octave bands.

RC = roomCriteria(___,Name=Value) specifies options using one or more name-value arguments.

[RC,LMF] = roomCriteria(___) also returns the mid-frequency average (LMF).

[RC,LMF,QAI] = roomCriteria(___) also returns the quality assessment index (QAI).

[RC,LMF,QAI,rattleRisk] = roomCriteria(___) also returns a structure detailing the likelihood of acoustically induced vibrations and rattles.

roomCriteria(___) without any output arguments plots the octave band SPL measurements against RC curves and displays the RC level.

Examples

Room Criteria Evaluation from Room Recording

Load a recording of a room with background noise.

[audioIn, fs] = audioread("office_kitchen_44p1_20s.wav");

If possible, enter the calibration factor for the microphone used to make the recording or calculate it using calibrateMicrophone. The microphone in this example has an associated reference recording at 1 kHz with an SPL meter reading of 64 dB.

[audioRef, fsRef] = audioread("1khz_64db_44p1.wav");
SPLreading = 64;
calibrationFactor = calibrateMicrophone(audioRef,fsRef,SPLreading)

calibrationFactor = 
2.0836

Plot the room criteria (RC) level for the room recording.

roomCriteria(audioIn,fs,CalibrationFactor=calibrationFactor)

This room has an RC level of 41, with a spectrum imbalance characterized by hiss caused by high frequencies. Additionally calculate the mid-frequency average (LMF), quality assessment index (QAI), and analyze the room for spectrum imbalances and rattle risk.

[RC, LMF, QAI, rr] = roomCriteria(audioIn,fs,CalibrationFactor=calibrationFactor)

RC = 
"RC-41 (H)"

LMF = 
40.9815

QAI = 
10

rr = struct with fields:
    Summary: "No acoustically induced vibrations and rattles issues detected."
    Details: [3×3 table]

Room Criteria Evaluation of SPL Meter Readings

Collect equivalent continuous sound level (Leq) measurements of a room using a sound pressure level (SPL) meter with octave band filters centered at 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000, and 8000 Hz.

Leq = [59,61,54,47,38,37,30,24,19,12]; % readings from meter

Use roomCriteria to calculate the room criteria (RC) level using the readings from the SPL meter.

RC = roomCriteria(Leq)

RC = 
"RC-30 (R)"

Input Arguments

audioIn — Audio signal

column vector

Audio input, specified as a column vector of real finite numbers. If audioIn is not calibrated, you can determine the calibration factor using calibrateMicrophone. Specify either audioIn or Leq.

For guidance on taking compliant measurements, see Calibration Factor for Audio Recordings.

Data Types: single | double

fs — Sample rate (Hz)

positive scalar

Sample rate in Hz, specified as a scalar equal to or greater than 16 kHz.

fs is required when you specify the first argument as audioIn. This argument is invalid when you specify the first argument as Leq.

Data Types: single | double

Leq — Octave-band equivalent continuous SPL measurements

1-by-10 row vector

Octave-band equivalent continuous sound level (Leq) measurements in decibels (dB), specified as a 10-element row vector. Each element must correspond to a measurement at nominal octave band center 16, 31.5, 63, 125, 250, 500, 1000, 2000, 4000, and 8000 Hz, respectively.

If the SPL for a given band is unknown, specify it as missing. An RC level calculated with missing Leq values might not be compliant with ASA S12.2-2019.

Specify either audioIn or Leq.

For guidance on taking compliant measurements, see Obtaining Standard Compliant Sound Level Measurements.

Dependencies

Data Types: single | double

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: roomCriteria(audioIn,fs,CalibrationFactor=1.5)

CalibrationFactor — Microphone calibration factor

1 (default) | positive scalar

Microphone calibration factor, specified as a positive scalar. audioIn is multiplied by CalibrationFactor before analysis. To compute the calibration factor specific to your system, use the calibrateMicrophone function.

CalibrationFactor is valid only when you specify the first argument as audioIn.

Data Types: single | double

PressureReference — Reference pressure (Pa)

20e-6 (default) | positive scalar

Reference pressure for dB calculation in pascals, specified as a positive scalar. The default value, 20 micropascals, is the common value for air.

PressureReference is valid only when you specify the first argument as audioIn.

Data Types: single | double

Output Arguments

RC — Room criteria rating

string

RC level, returned as a string. RC has the form RC-LMF (SC), where LMF is the mid-frequency average value of the input rounded to the nearest decibel and SC is the spectrum classification.

For more information on the calculating the RC value, see Calculating the RC Level and Spectrum Imbalance.

LMF — Mid-frequency average

scalar

Mid-frequency average, returned as a scalar. The mid-frequency average is the average of the SPL measurements in the 500, 1000, and 2000 Hz octave bands.

For more information, see Mid-Frequency Average.

QAI — Quality assessment index

scalar

Quality assessment index, returned as a scalar. The QAI is a measure of the degree to which the shape of the spectrum of the input deviates from the selected RC curve.

For more information on spectrum imbalance determination, see Quality Assessment Index.

rattleRisk — Risk of acoustically induced vibrations and rattles

structure

Risk of acoustically induced vibrations and rattles, returned as a structure. rattleRisk contains a summary of octave bands that can contain perceptible rattle and the table of values used by the function to determine the risk.

For more information on rattle risk, see Rattle Risk

More About

Calibration Factor for Audio Recordings

Calibrating the input before calling roomCriteria using an audio file is recommended for more accurate results. Record a 1 kHz tone using the reference microphone and note the SPL reading from a compliant SPL meter. Use the calibrateMicrophone function to obtain the calibration factor.

The diagram shows a typical setup for microphone calibration. For room noise evaluation, use Z frequency-weighting (some meters use the label linear or flat).

Obtaining Standard Compliant Sound Level Measurements

The ANSI/ASA S12.2-2019 [1] standard does not provide explicit guidelines for gathering measurements for RC Mark II metric. However, the following guidance is provided for the related NC and RNC metrics:

• Measure near the average standing or seating height for the expected room occupants.

• The microphone or meter must be at least 0.6 m from any acoustically reflective surface, 1.2 m from the intersection of any two surfaces, and 2.4 m from the intersection of any three surfaces.

• Record Leq measurements using a standard-compliant integrating-averaging meter set to fast time weighting and flat (Z-weighted) frequency weighting. For more information, see splMeter.

• Take measurements at a specific point of interest or using a slow sweep around the entire space.

• Record audio or measurements for at least 20 seconds when sweeping around the space.

Mid-Frequency Average

The mid-frequency average (LMF) is defined in the standard [1] as the mean of the 500, 1000, and 2000 Hz Leq measurements in decibels:

$$\text{LMF}=\frac{1}{3}\left(L_{500}+L_{1000}+L_{2000}\right)\text{.}$$

Calculating the RC Level and Spectrum Imbalance

RC curves [1] are primarily used to evaluate background noise in indoor spaces where the main sources of noise are HVAC systems. Each curve is defined by SPL values in dB for octave bands 16 Hz through 8000 Hz in Table D.1 of the standard.

An RC curve is chosen based on the LMF of input measurements, rounded to the nearest decibel. The spectrum imbalance is determined by the difference between the observed octave band measurements and the selected RC curve. The table lists the possible spectrum designations.

Classification (Label)	Criteria
Neutral (N)	No SPL measurements in the 500 Hz octave band or below exceed the selected RC curve by more than 5 dB. No SPL measurements in the 1000 Hz octave band or above exceed the selected RC curve by more than 3 dB. Neutral is the only acceptable spectrum classification in most scenarios.
Rumble (R)	One or more measurements in the 500 Hz octave band or below exceed the selected RC curve by more than 5 dB.
Hiss (H)	One or more measurements in the 1000 Hz octave band or above exceed the selected RC curve by more than 3 dB.
Perceptible vibration and rattle (RV)	Any measurement in the 16, 31.5, or 63 Hz octave band exceeds the threshold for moderately noticeable rattle (see Rattle Risk).

Quality Assessment Index

The quality assessment index (QAI) is a measure of how much the observed SPL measurements deviate from the selected RC curve [2]. The QAI is computed using three spectral deviations, computed as

$$\begin{array}{l}{\text{SD}}_{\text{L}}=10{\log }_{10}\left(\frac{1}{3}\left({10}^{\Delta L_{16}/10}+{10}^{\Delta L_{31.5}/10}+{10}^{\Delta L_{63}/10}\right)\right)\\ {\text{SD}}_{\text{M}}=10{\log }_{10}\left(\frac{1}{3}\left({10}^{\Delta L_{125}/10}+{10}^{\Delta L_{250}/10}+{10}^{\Delta L_{500}/10}\right)\right)\\ {\text{SD}}_{\text{H}}=10{\log }_{10}\left(\frac{1}{3}\left({10}^{\Delta L_{1000}/10}+{10}^{\Delta L_{2000}/10}+{10}^{\Delta L_{4000}/10}\right)\right)\text{,}\end{array}$$

where ΔL_f is the difference between the observed measurements and the RC curve at the octave band with center frequency f. The QAI is defined as the difference between the maximum spectral deviation and the minimum spectral deviation.

Rattle Risk

According to the ANSI/ASA S12.2-2019 [1] standard, if Leq measurements in the low frequency octave bands exceed the values in the table, acoustically induced vibrations and rattles are likely.

Octave Band	16 Hz	31.5 Hz	63 Hz
Clearly perceptible vibration and rattles likely	75 dB	75 dB	80 dB
Moderately perceptible vibration and rattles likely	65 dB	65 dB	70 dB

References

[1] Acoustical Society of America. Criteria for Evaluating Room Noise. ANSI/ASA S12.2-2019 (R2023). Acoustical Society of America, 2019.

[2] Blazier, Jr., Warren E. “RC Mark II: A Refined Procedure for Rating the Noise of Heating, Ventilating, and Air-Conditioning (HVAC) Systems in Buildings.” Noise Control Engineering Journal 45, no. 6 (1997): 243. https://doi.org/10.3397/1.2828446.

Version History

Introduced in R2026b