The SansAmp, however, took the amp-and-speaker-in-a-box concept to an entirely new level of sophistication. Its design incorporates a complete, miniature, push-pull output stage, combined with a preamp, plus emulation of the characteristic response of a typical guitar speaker, with further response shaping from a microphone and its placement. The effects of a phase-inverter stage and output transformer were also simulated, all in solid-state, analogue circuitry. The prototype incorporated an eight-way DIP switch at its heart, apparently just to help the designer home in on the best sound for DI recording, and the story is that he was persuaded to retain that in the final product by one of his 'big-name' test guitar players. Thus, one of the most distinctive and important features of the idiosyncratic original SansAmp was born. Finding that no-one wanted to licence and manufacture his invention, Andrew Barta decided to make it himself, using the name Tech 21, and raised the bar in the field of direct electric guitar recording to a new level.
The AC electric motor used in a VFD system is usually a three-phase induction motor. Some types of single-phase motors or synchronous motors can be advantageous in some situations, but generally three-phase induction motors are preferred as the most economical. Motors that are designed for fixed-speed operation are often used. Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1.
The VFD controller is a solid-state power electronics conversion system consisting of three distinct sub-systems: a rectifier bridge converter, a direct current (DC) link, and an inverter. Voltage-source inverter (VSI) drives (see 'Generic topologies' sub-section below) are by far the most common type of drives. Most drives are AC-AC drives in that they convert AC line input to AC inverter output. However, in some applications such as common DC bus or solar applications, drives are configured as DC-AC drives. The most basic rectifier converter for the VSI drive is configured as a three-phase, six-pulse, full-wave diode bridge. In a VSI drive, the DC link consists of a capacitor which smooths out the converter's DC output ripple and provides a stiff input to the inverter. This filtered DC voltage is converted to quasi-sinusoidal AC voltage output using the inverter's active switching elements. VSI drives provide higher power factor and lower harmonic distortion than phase-controlled current-source inverter (CSI) and load-commutated inverter (LCI) drives (see 'Generic topologies' sub-section below). The drive controller can also be configured as a phase converter having single-phase converter input and three-phase inverter output.
The carrier-frequency pulsed output voltage of a PWM VFD causes rapid rise times in these pulses, the transmission line effects of which must be considered. Since the transmission-line impedance of the cable and motor are different, pulses tend to reflect back from the motor terminals into the cable. The resulting reflections can produce overvoltages equal to twice the DC bus voltage or up to 3.1 times the rated line voltage for long cable runs, putting high stress on the cable and motor windings, and eventual insulation failure. Insulation standards for three-phase motors rated 230 V or less adequately protect against such long-lead overvoltages. On 460 V or 575 V systems and inverters with 3rd-generation 0.1-microsecond-rise-time IGBTs, the maximum recommended cable distance between VFD and motor is about 50 m or 150 feet. For emerging SiC MOSFET powered drives, significant overvoltages have been observed at cable lengths as short as 3 meters. Solutions to overvoltages caused by long lead lengths include minimizing cable length, lowering carrier frequency, installing dV/dt filters, using inverter-duty-rated motors (that are rated 600 V to withstand pulse trains with rise time less than or equal to 0.1 microsecond, of 1,600 V peak magnitude), and installing LCR low-pass sine wave filters. Selection of optimum PWM carrier frequency for AC drives involves balancing noise, heat, motor insulation stress, common-mode voltage-induced motor bearing current damage, smooth motor operation, and other factors. Further harmonics attenuation can be obtained by using an LCR low-pass sine wave filter or dV/dt filter.
Prevention of high-frequency bearing current damage uses three approaches: good cabling and grounding practices, interruption of bearing currents, and filtering or damping of common-mode currents for example through soft magnetic cores, the so-called inductive absorbers. Good cabling and grounding practices can include use of shielded, symmetrical-geometry power cable to supply the motor, installation of shaft grounding brushes, and conductive bearing grease. Bearing currents can be interrupted by installation of insulated bearings and specially designed electrostatic-shielded induction motors. Filtering and damping high-frequency bearing can be done though inserting soft magnetic cores over the three phases giving a high frequency impedance against the common mode or motor bearing currents. Another approach is to use instead of standard 2-level inverter drives, using either 3-level inverter drives or matrix converters.
This is most common during multi-microphone recordings because of time variations between the source and its sound waves being captured by each microphone. The other thing that can cause phase cancellation is polarity.
PI by sound radix is an impressive tool that enhances mixes with phase interaction, giving users the possibility to achieve the best possible correlation within the mix, improving the overall quality on a whole different level.
Noise canceling headphones work by recording sound and playing a phase inverted sound to cancel it. With a laptop the mic first off sucks, and nicely in front of you this means sound coming from behind you will reach your ears first before it even hits the mic. Then it has to go through the computer onto the slow soundcard (likely a ping of .1 seconds or more) to the speakers where it'll play. This lag time will be too great to deal with.So it comes down to mainly this:You and the mic hear different things (in headphones they are in your ears).Lag time from standard laptop sound cards is big, you often can't even get a guitar amp working well for this reason over your computer (near 0 in the headphones).
If the sound you need to cancel is consistent, for example inside an airplane or the hum of a factory, it seems like the computer's lag shouldn't matter, because the sound is the same no matter how late it arrives. The key would be to accurately phase shift the resulting sound in your headphones. For example, one might try adjustable phase shifting software such as on -vst-effects-2/phase-shifter
It should be possible for a constant sound (eg: fan bearing whine), but as other pointed out, for regular variable sound background environments, it surely won't work well with common hardware and software.
I also strongly doubt the software would have any reliable way of measuring the lag with high precision (for calibration), which is crucial for sound cancelling waves. (Edit: except maybe for doing manual calibration of phase.) 2b1af7f3a8