Key result
A real-time frequency shifter implemented on a VLIW DSP platform provided a clear improvement in heartbeat perception in noisy environments compared to unprocessed sounds.
Why the study?
Heart sound auscultation is limited by external noise and low-frequency bandwidth where human hearing sensitivity is poor, requiring spectrum shifting to higher frequencies to improve perception.
A novel real-time frequency shifter implemented on a DSP platform significantly improves the acoustic perception of heart sounds in noisy environments while reducing computational and memory requirements.
May improve heart sound perception in noise; leaves open clinical validation of this Hilbert-based shifter.
Auscultation of heart sounds is important to perform cardiovascular assessment. External noises may limit heart sound perception. In addition, heart sound bandwidth is concentrated at very low frequencies, where the human ear has poor sensitivity. Therefore, the acoustic perception of the operator can be significantly improved by shifting the heart sound spectrum toward higher frequencies. This study proposes a real-time frequency shifter based on the Hilbert transform. Key system components are the Hilbert transformer implemented as a Finite Impulse Response (FIR) filter, and a Direct Digital Frequency Synthesizer (DDFS), which allows agile modification of the frequency shift. The frequency shifter has been implemented on a VLIW Digital Signal Processor (DSP) by devising a novel piecewise quadratic approximation technique for efficient DDFS implementation. The performance has been compared with other DDFS implementations both considering piecewise linear technique and sine/cosine standard library functions of the DSP. Piecewise techniques allow a more than 50% reduction in execution time compared to the DSP library. Piecewise quadratic technique also allows a more than 50% reduction in total required memory size in comparison to the piecewise linear. The theoretical analysis of the dynamic power dissipation exhibits a more than 20% reduction using piecewise techniques with respect to the DSP library. The real-time operation has been also verified on the DSK6713 rapid prototyping board by Texas Instruments C6713 DSP. Audiologic tests have also been performed to assess the actual improvement of heart sound perception. To this aim, heart sound recordings were corrupted by additive white Gaussian noise, crowded street noise, and helicopter noise, with different signal-to-noise ratios. All recordings were collected from public databases. Statistical analyses of the audiological test results confirm that the proposed approach provides a clear improvement in heartbeat perception in noisy environments.
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Muto et al. (2023) studied Healthy volunteers (evaluating heart sound perception) (n=41). Real-time frequency shifter (50 Hz and 100 Hz shift) vs. Unprocessed heart sounds was evaluated on Minimum signal-to-noise ratio (SNRmin) for reliable heart sound perception. A real-time frequency shifter implemented on a VLIW DSP platform provided a clear improvement in heartbeat perception in noisy environments compared to unprocessed sounds.
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