Measuring Acoustic Transfer Functions - Swapan Gandhi and Juan Sierra (Meyer Sound)

We often want to characterize an audio system but we might not have access to the underlying input signal,  This occurs in common devices that have their own clocks and unknown latency. Our friends at Meyer Sound have this problem and are proposing a solution based on a "virtual referece." Grounded in their experience measuring and tuning room acoustics, they will share with us details of their method and a live demonstration of its use to characterize some popular consumer audio devices.

Who:  Swapan Gandhi and Juan Sierra (Meyer Sound)
What: Transfer Function Measurements When the Reference Signal is Known but not Accessible
When: Friday October 18 at 10:30AM
Where: CCRMA Seminar Room, Top Floor of the Knoll at Stanford
Why: Metrics are important

Swapan Gandhi and Juan Sierra (Meyer Sound)

The current boom in personal listening devices such as over the counter hearing aids, augmented reality devices, and Bluetooth headsets, has created a need for developers and researchers to understand what exactly these devices are doing to the audio. Transfer functions via the dual FFT method (magnitude, phase and coherence) are a useful tool for system identification however typically they require both the input reference signal to the system under test and its output. The reference signal is usually duplicated into an analyzer using a y-cable (or equivalent) along with the output of the system being identified. Alternatively, the analyzer could play a reference signal into an input to the system.

However, neither of these options are easily available for most of these listening devices. We will demonstrate a new method called “Virtual Reference” which provides a reference signal to an analyzer simply by virtue of having a digital copy of the reference signal which is to be played on the system under test. The analyzer watches the output signal of the system only, calculates various metrics in comparison to the stored reference signal, and then begins playing its own copy when the calculated metrics exceed a trigger threshold. This virtual reference signal then allows single-ended measurement of transfer functions. In addition, due to isolation of the clock driving the virtual reference signal this method allows estimation of the playback rate and jitter statistics of the system under test.

Biographies:


Swapan Gandhi is a professional musician and an Auditory Researcher in Meyer Sound’s R&D team where he works on a broad range of scientific projects at the intersection of physics and human perception. He has an extensive background in scientific computing and psychoacoustics acquired while working as a researcher in the Hafter Auditory perception Lab at UC Berkeley where he received a degree in physics and on the research team at Starkey Hearing Technologies.

Juan Sierra is a PhD Candidate in Music Technology at NYU and am currently based in NYUAD as part of the Global Fellowship program. As a professional musician, his expertise lies in Audio Engineering, and he hold a master's degree in Music, Science, and Technology from the prestigious Center for Computer Research in Music and Acoustics (CCRMA) at Stanford University. His extensive knowledge in production, music recording, and mixing is often supplemented by his deep understanding of physics and mathematics, which has enabled him to create exceptional projects in acoustics, digital signal processing, and software development. This knowledge forms the foundation of his precise and meticulous workflow without compromising on emotivity and artistic expression.