Distortion Analysis PDF

Distortions Under the heading of distortions different types of signal change are summarized. It is generally differentiate: Linear Distortions Nonlinear Distortions Linear Distortion The term "linear distortion" refers primarily to irregularities of the frequency response. Our listening...

Distortions Under the heading of distortions different types of signal change are summarized. It is generally differentiate: Linear Distortions Nonlinear Distortions Linear Distortion The term "linear distortion" refers primarily to irregularities of the frequency response. Our listening range from 20 Hz to 20 kHz is considered the basis of observation. Almost all real systems have more or less strong linear distortions of the amplitude frequency response. Especially the edge areas are often affected by such disturbances.Most often, the amplitude response falls slightly at the upper and lower end. An exception may be tape machines where the amplitude frequency response increases towards the highs. Exemplary frequency response for an analog device Exemplary, simplified frequency response of a tape machine Deviations of the phase frequency response also fall into the group of linear distortions. Nonlinear Distortion Nonlinear distortions are distortions of the transmitted waveform. They show up as 'deformation' of the waveform at the input. They arise when a transmission element can not follow the voltage curve exactly. Metrologically, such a change in the waveform is expressed by additional overtones. Sinus Wave 100 Hz no distortion Sinus Wave 100 Hz, strong distortion – visible overtones, especially odd ones Overtone Series The distortion of a sinusoidal oscillation with the frequency f1 produces new oscillations with the frequencies: 2f1, 3f1, 4f1 … These vibrations are called harmonics or overtones. They are divided into Even: 2f1, 4f1, 6f1 … And Odd: 3f1, 5f1, 7f1... From a subjective point of view, even overtone series (for example in tube circuits) usually sound more pleasant than odd (they occur, for example, in many transistor circuits). The audibility of such nonlinear distortions is difficult to assess. On the one hand, natural sounds already have such complex overtone series that additional distortion products must already have very high levels in order to become clearly perceptible in the superposition. On the other hand, distortions are not always directly perceived as a disturbance, but can make a sound sound more appealing (fuller, more brilliant, more direct). Especially even distortions are therefore often used as a stylistic device (tube distortion, tape machine distortions). In addition, distortions are used as significant effects. Every guitarist knows the classic distortion, overdrive and fuzz effects. Distortion Compression Since such effects are caused by a strong overdriving of an amplifier component (tube, transistor), in addition to the generation of harmonic overtones to a strong compression of the signal occurs. Undistorted Distorted This compression effect is very strong for distortion devices. However, less severe overdrives (e.g., in tube circuits and magnetic tape machines) often result in a compression effect. In this case, the signal is guided only slowly into the boundary region of the amplifier element, so that the compression effects increase steadily. One speaks of saturation, if one leads a component into its upper border area. The transfer characteristic is flattened upwards: Total Harmonic Distortion (THD) The measurement of nonlinear distortion takes place via the so-called harmonic Distortion. The harmonic distortion k indicates the proportion the occurring distortion products have in the complete signal. Therefore, k is dimensionless; it is given as a percentage: It is important that the calculation is done with the rms values of the voltages and not with the peak values! Since every single harmonic would have to be included in the measurement of k, most harmonic distortion data are limited to the calculation for the first two harmonics. These are called k2 and k3. For practical measurements, care must therefore be taken to see whether the specified harmonic distortion factor takes into account the total harmonic distortion k or only the partial distortion factors k2 or k3. In practice: This simplification is therefore valid, since the limit values for the harmonic distortion are so small that the further harmonics would scarcely influence the value. Intermodulation Distortion The previously described distortion products are in harmonic relation to the fundamental oscillation. This observation does not apply to so-called intermodulation products. If a system is burdened with more than a single sinusoid (i.e. a complex oscillation), additional frequencies may arise, which are in a mathematical but harmonic relationship to the partial tones at the input. They represent the sum and difference tones of the individual original oscillation. Our hearing reacts very sensitively to such intermodulation products. Especially with speakers and power amplifiers, it is therefore important to pay attention to the smallest possible proportion of this type of distortion. Unfortunately, very few manufacturers report measurements for this disorder. Two sine waves of the same level are used for the measurement. A frequency analysis shows the resulting interfering products: The calculation of intermodulation distortions is very complex and hardly used in the audio engineering practice. In addition, the difficulty arises to determine limits. The rule is: the less, the better. For professional active speakers, the orientation value is: less than 2%! For high-quality active loudspeakers, values up to 0.5% are used as an orientation value.