Heidi-Maria Lehtonen

Fast automatic inharmonicity estimation algorithm

A new algorithm is presented for estimating the inharmonicity coefficient of slightly inharmonic stringed instrument sounds. In the proposed partial frequencies deviation method, the inharmonicity is estimated in an intuitive way by minimizing the deviation of the expected partial frequencies compared to the frequencies of the high amplitude peaks in the spectrum. This is done in an iterative process, where the algorithm converges towards the target estimation value. The algorithm is tested using both synthetic and recorded piano tones. The results show that the new algorithm produces accurate results with a small computation cost compared to other methods.

Analysis and modeling of piano sustain-pedal effects

This paper describes the main features of the sustain-pedal effect in the piano through signal analysis and presents an algorithm for simulating the effect. The sustain pedal is found to increase the decay time of partials in the middle range of the keyboard, but this effect is not observed in the case of the bass and treble tones. The amplitude beating characteristics of piano tones are measured with and without the sustain pedal engaged, and amplitude envelopes of partial overtone decay are estimated and displayed. It is found that the usage of the sustain pedal introduces interesting distortions of the two-stage decay. The string register response was investigated by removing partials from recorded tones; it was observed that as the string register is free to vibrate, the amount of sympathetic vibrations is increased. The synthesis algorithm, which simulates the string register, is based on 12 string models that correspond to the lowest tones of the piano. The algorithm has been tested with recorded piano tones without the sustain pedal. The objective and subjective results show that the algorithm is able to approximately reproduce the main features of the sustain-pedal effect.

Canceling and selecting partials from musical tones using fractional-delay filters

Using Fractional-Delay Filters Heidi-Maria Lehtonen,* Vesa Valimaki,* and Timo I. Laakso*f * Helsinki University of Technology (TKK) Department of Signal Processing and Acoustics P.O. Box 3000, FI-02015 TKK, Espoo, Finland +National Board of Patents and Registration of Finland Patents and Innovations Line P.O. Box 1140, FI-00101, Helsinki, Finland (heidi-maria.lehtonen, vesa.valimaki, timo.laakso}® tkk.fi

Sparse multi-stage loss filter design for waveguide piano synthesis

A new filter structure and a design method are proposed for the loss filter that is used in digital waveguide synthesis. The main application of this work is the sound synthesis of the piano, but the methods are also applicable to the synthesis of other struck or plucked string instruments. The filter structure is an extension of a sparse FIR filter called the ripple filter, which has been proposed previously for waveguide synthesis of keyboard instruments. The new structure is based on a cascade of sparse FIR filters, which are designed one after the other on subbands that are integer fractions of the audio range. We show by examples that a cascade of three digital filters provides possibilities to exactly match the decay rate of a finite number, such as 50, lowest-order partials, or to approximately match the general trend and some variations of many partials of a piano tone. The subfilters can easily be designed using standard techniques

A parametric piano synthesizer

Synthesizer Jukka Rauhala,∗ Mikael Laurson,† Vesa Valimaki,∗ Heidi-Maria Lehtonen,∗ and Vesa Norilo† ∗Department of Signal Processing and Acoustics Helsinki University of Technology P.O. Box 3000, FI-02015 TKK, Espoo, Finland www.acoustics.hut.fi jukkis@acoustics.hut.fi, {vesa.valimaki, heidi-maria.lehtonen} @tkk.fi †Centre for Music and Technology Sibelius Academy P.O. Box 86, FI-00251, Helsinki, Finland cmt.siba.fi {laurson, vnorilo}@siba.fi

Audibility of aliasing distortion in sawtooth signals and its implications for oscillator algorithm design.

This paper investigates the audibility threshold of aliasing in computer-generated sawtooth signals. Listening tests were conducted to find out how much the aliased frequency components below and above the fundamental must be attenuated for them to be inaudible. The tested tones comprised the fundamental frequencies 415, 932, 1480, 2093, 3136, and 3951 Hz, presented at 60-dB SPL and 44.1-kHz sampling rate. The results indicate that above the fundamental the aliased components must be attenuated 0, 19, 26, 27, 32, and 41 dB for the corresponding fundamental frequencies, and below the fundamental the attenuation of 0, 3, 6, 11, 12, and 11 dB, respectively, is sufficient. The results imply that the frequency-masking phenomenon affects the perception of aliasing and that the masking effect is more prominent above the fundamental than below it. The A-weighted noise-to-mask ratio is proposed as a suitable quality measure for sawtooth signals containing aliasing. It was shown that the bandlimited impulse train, the differentiated parabolic waveform, and the fourth-order polynomial bandlimited step function synthesis algorithms are perceptually alias-free up to 1, 2, and 4 kHz, respectively. General design rules for antialiasing sawtooth oscillators are derived based on the results and on knowledge of level-dependence of masking.

Toward Next-Generation Digital Keyboard Instruments

In this article, alternative approaches to digital keyboard instrument synthesis are looked into. Physics-based sound synthesis, which aims at generating natural-sounding musical instrument tones algorithmically without using a large sample database, is a promising approach. It would provide high-quality music synthesis to systems that cannot afford a large memory, such as mobile phones and portable electronic games. The realistic parametric synthesis of musical instrument sounds is still a challenge, but physical modeling techniques introduced during the last few decades can help to solve it. Recently, the first commercial products have been introduced, for example, by Pianoteq. Three keyboard instruments, the clavichord, the harpsichord, and the grand piano, are focused on here. The sound production principles and acoustics of these instruments are first discussed. Then, the previous parametric synthesis algorithms developed for these instruments are reviewed. The remaining part of this article concentrates on new signal processing methods for parametric synthesis of the piano

A Perceptual Study on Velvet Noise and Its Variants at Different Pulse Densities

This paper investigates sparse noise sequences, including the previously proposed velvet noise and its novel variants defined here. All sequences consist of sample values minus one, zero, and plus one only, and the location and the sign of each impulse is randomly chosen. Two of the proposed algorithms are direct variants of the original velvet noise requiring two random number sequences for determining the impulse locations and signs. In one of the proposed algorithms the impulse locations and signs are drawn from the same random number sequence, which is advantageous in terms of implementation. Moreover, two of the new sequences include known regions of zeros. The perceived smoothness of the proposed sequences was studied with a listening test in which test subjects compared the noise sequences against a reference signal that was a Gaussian white noise. The results show that the original velvet noise sounds smoother than the reference at 2000 impulses per second. At 4000 impulses per second, also three of the proposed algorithms are perceived smoother than the Gaussian noise sequence. These observations can be exploited in the synthesis of noisy sounds and in artificial reverberation.

Perception of longitudinal components in piano string vibrations

This paper investigates the audibility of longitudinal components in piano string vibrations with listening tests. The recorded fortissimo sounds of two grand and one upright pianos have been resynthesized with and without longitudinal components and used in ABX type listening tests. Results suggest that the longitudinal components are audible up to note C(5). However, a second test seeking the importance of the difference shows that the effect of longitudinal components for the range A(3)-C(5) is subtle. This means that modeling the phenomenon up to around note A(3) only is acceptable for sound synthesis applications.

Analysis of the part-pedaling effect in the piano

This letter reports basic acoustic phenomena related to part-pedaling in the piano. With part-pedaling, the piano tone can be divided into three distinct time intervals: initial free vibration, damper-string interaction, and final free vibration. Varying the distance of the damper from the string, the acoustic signal and the damper acceleration were measured for several piano tones. During the damper-string interaction, the piano tone decay is rapid and the timbre of the tone is affected by the nonlinear amplitude limitation of the string motion. During the final free decay, the string continues to vibrate freely with a lower decay rate.