Monofilament nylon strings with a range of diameters, commercially marketed as harp strings, have been tested to establish their long-term mechanical properties. Once a string had settled into a desired stress state, the Young’s modulus was measured by a variety of methods that probe different time-scales. The modulus was found to be a strong function of testing frequency and also a strong function of stress. Strings were also subjected to cyclical variations of temperature, allowing various thermal properties to be measured: the coefficient of linear thermal expansion and the thermal sensitivities of tuning, Young’s modulus and density. The results revealed that the particular strings tested are divided into two groups with very different properties: stress-strain behaviour differing by a factor of two and some parametric sensitivities even having the opposite sign. Within each group, correlation studies allowed simple functional fits to be found to the key properties, which have the potential to be used in automated tuning systems for harp strings.

The long-term mechanical behaviour of a number of fluorocarbon and gut harp strings has been examined, and the results compared with a previous study of rectified nylon strings. The stretching behaviour of the three materials was studied via different measures of the Young’s modulus; with test time scales on the order of weeks, minutes, and milliseconds. The strings were subjected to cyclic variations in temperature, enabling various aspects of their thermal behaviour to be investigated. The effects of humidity changes on gut strings were also examined. The behaviour of the fluorocarbon strings was found to be similar in many ways to that of the nylon strings, despite their different chemical formulation and significantly higher density. In particular, the faster measures of Young’s modulus were found to show an almost identical strong variation with the applied stress; while the thermal behaviour of both materials was largely determined by the balance between opposing effects associated with thermal contraction and thermal variations in the Young’s modulus. The gut strings showed some similarities of behaviour to the synthetic materials, but also major differences. All three measures of the Young’s modulus remained constant as the applied stress was increased. The gut strings were far more sensitive to changes in humidity than the synthetic materials, although some of the results, especially the thermal tuning sensitivity of the strings when held at constant length, displayed remarkable stability under changing humidity. The observed behaviour suggests very strongly that there is significant coupling between humidity-related changes in the linear density of a gut string and complementary changes in its tension.

The various factors constraining the choice of synthetic polymer and natural gut strings for musical instruments are discussed, including a newly-formulated constraint based on the internal damping of the string material. It is shown that all these constraints can be summarised graphically in a design chart, and calibrated versions of the chart are presented for monofilament strings of nylon, fluorocarbon and natural gut. Based on these charts, detailed case studies are presented for the stringing of a lute and a harp. An explanation is suggested for why harpists continue to favour gut over nylon.

After near-end crosstalk (NEXT), the principal problem with pulse amplitude modulation (PAM) is intersymbol interference (ISI). The author presents an analytical comparison of various recursive and nonrecursive subtractive equalization techniques which may be used to remove ISI. Properties of subscriber loop responses which may be used in the design of simple and efficient equalizers are also explored. Simulation results are presented comparing the performances of many of the described equalizer structures for an 800 kb/s 2B1Q PAM transmission system operating over 12 kft of 24 AWG cable

The use of a piezoelectric transducer to monitor the tuning of a musical instrument string has been investigated. It has been shown that the transverse resonance frequencies of the string can be identified by electrical measurements on a low-cost actuator/sensor, sufficiently discreetly to be done during a performance. This frequency measurement approach can be used as the basis for a tuning control mechanism to maintain a musical instrument string at the required pitch, without it having to be plucked or played. Such a system would be of direct benefit to harp players in particular, who have no other means to adjust a mistuned string during a performance. Some of the practical issues and implications of adding such a tuning control system to the harp are considered.

Natural gut harp strings are notoriously sensitive to changes in humidity, but the nature of this sensitivity is poorly understood. The results of some recent measurements are presented, in which a number of well-settled strings were held at constant temperature and subjected to changes in humidity. The results show multiple periods when, after raising the humidity, the strings appeared to undergo additional periods of creep. When the strings were not creeping, there appeared to be some form of coupling between humidity-induced changes in the string linear density and its tension. Moreover, the effects of these changes in linear density and tension largely cancelled out, with little net effect on the string frequency. The results presented here seem to indicate that the useful life of a gut harp string may be determined as much by its propensity to creep as by its inherent yield strength.