Sound Synthesis Using Programmable System-On-Chip Devices

The last 20 years has witnessed a resurgence of interest in analogue synthesisers 1 . Manufacturers, such as Moog and Sequential Circuits, that had disappeared from the commercial marketplace by the end of the 1980’s, have reappeared with an impressive line of products. Other established companies such as Korg and Roland, as well as entrants that had made their name with digital technology, such as Novation and Arturia, have released analogue instruments. Although the feature set of digital synthesisers is extensive and with a falling comparative cost, the analogue market has continued to grow with more and more devices coming available. They are perceived to be of superior sound quality by users, but their primary drawback is price, as numerous discrete components or specialist integrated circuits are required. This thesis introduces two novel low-cost approaches to building analogue-type synthesisers. Such a low-cost instrument could have applications in an educational laboratory environment for synthesisers. The first approach is to exploit a new mixed-signal technology called the Programmable System-on-Chip (PSoC), which includes a CPU core and mixed-signal arrays of configurable integrated analogue and digital peripherals. The second exploits a System on Chip (SoC) comprising an ARM-based (Acorn RISC Machine) processor and a Field-Programmable Gate Array (FPGA). Two synthesisers were built and were evaluated for difficulty of implementation and assessed for their sound quality. The design and testing process was recorded and documented in detail. The mixed-signal approach was found to be cheaper than the FPGA-approach both in terms of component costs and development time compared to the FPGA-based approach. Actually, the FPGA-approach was determined to be prohibitively expensive in terms of the development time incurred. The sound quality analysis demonstrated that both instruments were perceived by users to be of high quality, achieving a noticeable analogue sound. Future work would be to repackage the PSoC system and modules into rack-mounted form for use in an educational synthesiser laboratory environment

Fully stabilized mid-infrared frequency comb for high-precision molecular spectroscopy

A fully stabilized mid-infrared optical frequency comb spanning from 2.9 to 3.4 mu m is described in this article. The comb is based on half-harmonic generation in a femtosecond optical parametric oscillator, which transfers the high phase coherence of a fully stabilized near-infrared Er-doped fiber laser comb to the mid-infrared region. The method is simple, as no phase-locked loops or reference lasers are needed. Precise locking of optical frequencies of the mid-infrared comb to the pump comb is experimentally verified at sub-20 mHz level, which corresponds to a fractional statistical uncertainty of 2 x 10(-16) at the center frequency of the mid-infrared comb. The fully stabilized mid-infrared comb is an ideal tool for high-precision molecular spectroscopy, as well as for optical frequency metrology in the mid-infrared region, which is difficult to access with other stabilized frequency comb techniques. (C) 2017 Optical Society of AmericaPeer reviewe