Prominent Discrete Tones Research Articles

Study on tone-to-noise ratio calculation method for tones with frequency and amplitude variation

This paper is to present a method on improving consistency and accuracy of Tone-to-Noise Ratio (TNR) calculation for varying frequency tones in reporting prominent discrete tone according to ECMA-418-1. For given sound pressure spectrum, existing TNR calculation methods require suspect tones to be selected by the analyst, who must also determine the width of the tone, that could introduce significant uncertainty and variation between different analysts. Moreover, tones associated with unstable frequency could cause even more uncertainty in determining tone frequency band. In this study, an approach is proposed to determine the existence of discrete tone, define the tone frequency band, and lastly calculate TNR such that different analysts will be able to obtain consistent and more accurate TNR value. To validate the approach, several different noise spectra were used as mask noise, and thousands of numerically generated tones, with randomly varying frequencies and amplitudes, were modulated to the mask noise to generate synthesized waveform for TNR calculation. These randomly generated synthesized waveform were subjectively evaluated and confirmed that prominent discrete tone criteria are still applicable to tones with varying frequencies and amplitudes. The results show that proposed approach can significantly improve TNR calculation accuracy while ensure consistency between different analysts.

Revision of stand alone standard, ECMA-418-1 for the detection of prominent discrete tones using tone-to-noise ratio method and prominence ratio method

In 2020 December, ECMA-418-1 1st edition was published as a stand alone and dedicated standard that specifies two parallel detection methods for prominent discrete tones in noise emitted by Information Technology and Telecommunication Equipment. The two parameters are, so called, tone-to-noise ratio (TNR) and prominence ratio (PR), which were developed in an informative annex of ECMA-74, in 1980's and 1990's respectively. The 1st edition of ECMA-418-1, December 2020 was derived from ECMA-74:2019, Annex D. The 2nd edition was subsequently developed as minor revision, in 2022 December. And, the 3rd edition is planned for the end of 2023. This paper reviews the history of the technical challenges in the standardization both of TNR and PR, and mentions the standardization (clarification) of terminology planned for the third edition and other issues. In addition, differences from the similar standard, ISO/PAS 20065 etc. that were compared and contrasted during this standardization processes are also mentioned.

Experimental study on aerodynamic noise characteristics of high-lift configuration with variable gap leading-edge slat

The aircraft high-lift devices are important components to ensure the safety of take-off and landing, and it is also the main source of airframe noise in the process of take-off and landing, especially the leading-edge slat. The slat that reduces gap by rotating with the fixed axis is proposed in this paper, and experimental study of far-field aerodynamic noise characteristics of high-lift configuration with the slat is also carried out. The experimental results show that discrete tones in the low-middle frequency range disappear and the broadband frequency amplitude also slightly decline, resulting in a significant decrease in the overall sound pressure level of the high-lift configuration with slat gap of 0, compared with the configuration with conventional leading-edge slat. However, in the process of rotation from conventional slat to seamless slat, more prominent discrete tone in low-middle frequency range or humps in mid-high frequency range appear at angles of attack below 6°, which give rise to the overall increase in the sound pressure level. At angles of attack above 6°, these aero-acoustic phenomena are not obvious. Hence, the overall sound pressure levels of high-lift configuration gradually decrease with the rotation process in larger angles of attack.

Upcoming international standards in psychoacoustics

Besides loudness, other psychoacoustic parameters like tonality and roughness can be used for product noise assessments. Tonality measurement procedures quantify the audibility of prominent tonal components and roughness evaluates modulation characteristics. In June 2017, two new ISO standards for loudness were published: ISO 532-1 (Zwicker method, based on DIN 45631/A1:2010-03) for stationary and time-varying sounds and ISO 532-2 (Moore/Glasberg method, based on ANSI S3.4-2007) for stationary sounds only. Additionally, ISO TC 43/WG 9 started now to work on ISO 532-3 for time-varying loudness based on the TVL model of Moore/Glasberg. For many years, tonality measurement procedures such as the Tone-to-Noise Ratio (TNR) and Prominence Ratio (PR) have been applied to identify prominent discrete tones. Recently, a new perceptually accurate tonality assessment method based on a hearing model of Sottek was developed which evaluates the nonlinear and time-dependent loudness of both tonal and broadband components, separating them via the autocorrelation function. This new perception-model-based procedure, suitable for identifying and ranking tonalities from any sources, is proposed for the next edition of ECMA-74 as an alternative to TNR and PR. Furthermore, it is planned to extend ECMA-74 by a roughness calculation procedure based on the same hearing model approach together with some post processing (such as a weighted modulation spectral analysis). The paper gives an overview of recent developments of psychoacoustic standards.

Updates on Prominent Discrete Tone Procedures in ISO 7779, ECMA 74, and ANSI S1.13

There are two alternative procedures for determining if a tone is prominent, i.e. a "prominent discrete tone" in ISO 7779, ECMA 74 and ANSI S1.13: the Tone to Noise Ratio (TNR) method and the Prominence Ratio (PR) method. Both of these procedures have been used by the computer industry for more than a decade. Recent revisions to these procedures have refined the calculation of the critical bandwidth and modified the both procedures for low level tones. This paper describes these changes and the rationale behind them. Examples are presented that demonstrate the features of each procedure. The paper presents an overview on the applicability and limitations of each procedure.

Implementation of ISO 1996‐2 (2007) pure tone assessment in a sound level meter

Noise can be said to be tonal if it contains a distinguishable, discrete, continuous note. This may include a whine, hiss, screech, hum, etc., and any such subjective finding is open to discussion when reported. This is important when it is considered that the likelihood of a noise‐provoking complaint depends on its relative level to background, and whether or not it has certain audible characteristics. Fortunately, ISO 1996‐2 (2007) provides objective FFT (engineering) and 1/3‐octave band (survey) assessment procedures to be used to verify the presence of audible tones if their presence is in dispute. Bruel & Kjaer has implemented the methodology of ISO 1996‐2 in relation to assessing the audibility of prominent discrete tones in environmental noise into its innovative 2250 and 2270 hand‐held analysers. This paper describes the implementation in hand‐held instrumentation.

Comparison of various procedures for the assessment of prominent discrete tones using a large number of sound samples

The procedures from the standards ISO 1996-2 and DIN 45681 as well as the two procedures (TNR and PR) from ISO 7779 are compared. In the first section, characteristic features of the procedures (e.g. signal analysis parameters, degree of automation and characteristics of the prominent discrete tone analysis) are compared. In the second section, the procedures are applied to approximately 70 sound samples. Besides natural sounds (e.g. from machines), synthetic sounds (e.g. peak in a trough) are also used. The results are compared against assessments of the sounds by human subjects. The results of the comparisons are discussed, with special attention paid to cases where significant deviations occur. The third section looks at the results of the comparisons under the aspect of requirements for a standard (e.g. robustness, precision). Overall it was determined that none of the procedures investigated provides optimal results for all sound samples.

Audibility threshold spectrum for prominent discrete tone analysis

To evaluate the annoyance of tonal components in noise emissions, ANSI S1.13 (for general purposes) and/or ISO 7779/ECMA-74 (dedicatedfor IT equipment) state two similar metrics: tone-to-noise ratio (TNR) and prominence ratio(PR). By these or either of these two parameters, noise of question with a sharp spectral peak is analyzed by high resolution FFF and classified as prominent when it exceeds some criterion curve. According to present procedures, however this designation is dependent on only the spectral shape. To resolve this problem, the author proposes a threshold spectrum of human ear audibility. The spectrum is based on the reference threshold of hearing which is defined in ISO 389-7 and/or ISO 226. With this spectrum, one can objectively define whether the noise peak of question is audible or not, by simple comparison of the peak amplitude of noise emission and the corresponding value of threshold. Applying the threshold, one can avoid overkilling or unnecessary action for noise. Such a peak with absolutely low amplitude is not audible.

A comparison of two methods for the evaluation of prominent discrete tones: Phase 3

This paper presents results of Phase 3 of the study of prominent discrete tones by the Inter Committee Working Group (ICWG) from Information and Technology Equipment (ITTE). Progress and earlier results were reported at INTER-NOISE 99, the 139th Meeting of the Acoustical Society of America, and INTER-NOISE 2000. Phase 3 is a round robin involving 40 signals (some from ITTE products and some artificial sounds), which were recorded and distributed to participants as .wav files. Each of several ITTE company laboratories determined the objective tone-to-noise ratios and prominence ratios of the signals and/or provided subjective ratings. The paper presents comparisons of the objective and subjective ratings from the different laboratories. The relative success of the two objective methods in predicting the subjective ratings is discussed, as are the underlying issues and recommendations of the task group.

Psychoacoustic comparison of two methods for the evaluation of prominent discrete tones

Two objective methods have been developed to evaluate the potential annoyance of prominent discrete tones in the noise emissions of products: (1) the tone-to-noise ratio (TNR) method [ECMA-74-1997, ANSI S1.13-1995] and (2) the prominence ratio (PR) method [ANSI S1.13]. A task group of the Inter-Committee Working Group on noise from information technology and telecommunications equipment (ITTE) is studying both procedures, with the goal of optimizing a single method. In some cases the procedures give conflicting results, especially when there are harmonics and/or multiple tones within a single critical band. ECMA-74-1997 employs a modification of the TNR method for cases in which there are two tones within the critical band. This talk will present the results of two pilot studies comparing naive listeners’ subjective ratings of signals containing discrete tones to the measured TNR and PR values. In the first pilot study, stimuli were a series of recorded machine noises. In the second study, stimuli were constructed by mixing the noise produced by axial fans with a pure tone close to the fundamental frequency of the fans. The level and frequency of the tone was varied. The results of these pilot studies and recommendations for future work will be discussed.

Rating noise—The experience of the computer industry

With the general consensus of practicing noise control consultants that the two different sets of criterion curves for evaluating room noise contained in ANSI S12.2-1995 [room criterion (RC) and balanced noise criterion (NCB)] should be replaced with a single set of criterion curves, the authors believe that lessons can be learned from the computer industry, especially in accounting for noises with abnormal characteristics. This industry realizes that the noise emissions from their products should be compatible with the acoustical requirements of the environment in which the products are installed. The types of computer products cover a wide range with respect to functionality, size, sound power level, and spectral and temporal characteristics of their emissions. The rooms in which these products are installed also cover a wide range, including many types with significantly different levels of acceptable noise. In addition to using A-weighted descriptors (sound power level to describe product emissions and sound-pressure level to describe room noise levels), the computer industry has recognized the need to take into account and to characterize abnormal features of the noises, such as prominent discrete tones (ECMA-74-1996 or ANSI S1.13), tonal modulation or beating, and impulsive or fluctuating sounds. This paper presents some of these experiences from the computer industry in the context of establishing room noise criterion curves. [See NOISE-CON Proceedings for full paper.]

Measuring the sound power of a noise source and detecting pure tones with a single instrument combining true 1/3 octave band digital filters and an FFT analyzer

In the past, there has been a requirement for determination of both the sound power of sources and an investigation of the pure‐tone content. This is especially true in the computer and business equipment industry. Measurement of the sound power normally calls for standard (ANSI) class III 1/3 octave band filters, while pure‐tone determination requires narrow‐band (FFT) measurements; hence, two separate instrument systems were required. This paper describes a new instrument for these determinations in which the true standardized 1/3 oct filters and the FFT are combined. The procedure for automatically identifying prominent discrete tones per ANSI S12.10 is discussed.

Recent experience with the new ANSI S12.10‐198S procedure for identifying prominent discrete tones

The American National Standard for measuring noise emitted by business equipment, ANSI S12.10‐1985, includes a new procedure for identifying prominent discrete tones. The procedure is based upon comparing the sound pressure level in the tone to the sound pressure level in the Zwicker bandwidth centered around the tone. In general this new procedure is a substantial improvement over the previous procedure described in ANSI S1.29‐1979, and based on Appendix B of ANSI S.13, which uses sound pressure levels outside the Zwicker handwidth to determine the strength of the masking noise. However, after several months of use with a FFT analyzer it is dear that the S12.10 procedure raises questions that should be addressed. This paper presents examples of tones that sound prominent but do not calculate to be prominent by the new procedure, and examples that do not sound prominent but calculate to be prominent. This paper also presents limitations on use of one‐twelfth‐octave‐band filters to make the measurements required by the S12.10 procedure.

Identifying prominent discrete tones in noise emissions

Research has shown that broadband noise containing one or several discrete tones is usually judged more annoying than the same noise without the tones. In view of this, new noise emission standards are requiring that the presence or absence of prominent tones be reported along with the measured data. Therefore, it is imperative that a reliable accurate, and repeatable measurement method be available to identify and evaluate tones in noise. The methods described in current standards are based on the rather outdated, analog procedure that appeared in ANSI S 1.13 Appendix A (1971), but as a result of the growing use and affordability of modern digital signal processing instruments, new methods are now being proposed. One method [Noblie et al., Proceedings of NOISE-CON 85, Columbus, OH (June 1985)] is based on FFT measurements, while another is based on 1/12-octave-band analysis. This paper will review the concept of a prominent discrete tone, review the proposed new methods, and present comparisons of results from the different methods applied to actual machine noise.

How to use noise standards and what new standards are needed

The ISO 3740 series of basic standards for the determination of the sound power levels of stationary noise sources was issued by the International Organization for Standardization during the 1970s. American National Standards based on the ISO 3740 series have now been completed. These measurement standards have been adopted by several industries, including the manufacturers of computers and business equipment whose test code is continuously updated to reflect improvements in instrumentation and measurement methodology. Two important problems currently being addressed are the quantitative assessment of prominent discrete tones and the characterization of impulsive noise. The new standards being developed by the computer and business equipment industry are discussed with reference to current national and international requirements.