Drop sample tuning

Sample Rate Conversion Techniques. The simplest form of sample rate conversion is called either drop sample tuning or zero order hold interpolator. This technique is the basis for the table lookup phase increment oscillator, well known in computer music [Moore, 1990a],... 

Drop Sample Tuning table lookup sampling playback oscillator 323... 

We can look at an equivalent hardware block diagram. Here we have a wavetable being addressed by what is essentially a counter whose rate is changed to vary the pitch. The term drop sample tuning refers to the fact that samples are either dropped (skipped) or repeated to change the frequency of the oscillator. The phase increment is added to the current value of the phase register every sample, and the integer part of the phase is used as an address to lookup a sample in waveform memory to output to aDAC. 

Figure 8.5 Drop Sample Tuning table lookup sampling playback oscillator. The phase Increment Register adds an increment to the current phase, which has a fractional part and an integer part. The integer part is used to address a wavetable memory, and the fractional part is used to maintain tuning accuracy.

Drop sample tuning can introduce significant artifacts from changing the pitch of a waveform. This method originated in the design of early computer music oscillators... 

The airbrush needle and propellant gas pressure are adjusted to generate droplets of the appropriate size without shearing the cell or nucleus. An ink-glycerol mixture sprayed onto a pool of liquid on a glass slide, and measured, provides a convenient initial calibration. Fine tuning is done by spraying the actual sample onto a slide to make adjustments for viscosity and concentration. For isolated chicken erythrocyte nuclei, a pressure of 102 kPa produces 10-jum droplets, whereas whole cultured fibroblasts require a pressure of 81.6 kPa to provide 50-/im drops. 

Equation (8.3) shows that if the effective thickness of the polymer cloud I is to be maintained in the optimum range (- 1-10 /zm), then AT must be decreased as M is increased. Conversely, the temperature drop must be elevated for polymers of low molecular mass. The process of tuning AT to match the characteristics of the polymer sample requiring analysis can be illustrated by several examples from our laboratory. 

Retention in ThFFF is directly proportional to the temperature drop (AT) across the channel (see Eq. 1). The linear relationship between and AT holds even for moderate levels of retention (VVV° > 3). Having a predictable dependence of retention on AT means that AT can be efficiently tuned to optimize the trade-off between resolution and analysis time for each application. AT can also be varied over the course of a separation to resolve samples of extreme polydispersity in the most efficient manner. Decreasing AT over the course of a separation is analogous to temperature programing in gas chromatography or solvent programing in reversed-phase HPLC. 

The primary effect of this additional absorption loss in the laser cavity will be to reduce the laser output power. However, as the laser oscillation frequency is tuned towards the centre of the absorption line, the two holes burned in the population of absorbing atoms will start to overlap. At the line centre the population difference, and hence the absorption coefficient of the sample, is reduced by the saturation of atoms with zero axial velocity interacting with both components of the laser standing-wave field. This sharp drop in the absorption coefficient, which occurs about the centre of the absorption line, reduces the internal losses of the cavity and gives rise to a sharp increase in the power output of the laser. 

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