question: Why do strobe lights make a whine noise when charging?
comment: The flash operates at a very high voltage. Alas, it isn't powered by 200V batteries, as those are dangerous. To get the 200-300V needed from 3-6V worth of batteries, they use a transformer and an oscillator. That oscillator uses variable frequency, and the transformer has a tendency to vibrate just far enough that you can hear the sound.
passages: Although strobe lights are the most common use of trigger transformers, other devices such as arc lamps, gas laser tubes and even the common fluorescent light employ trigger transformers, however usually in a different form, such as using an electrical ballast to provide both the high voltage spike, as well as current limiting to prevent the tube from drawing excess current.
  
  Inductors are also commonly used in place of a trigger transformer, however are not considered transformers themselves, although similar in operation.
   A strobe without a capacitor storage device simply discharges mains voltages across the tube once it's fired. This type of strobe requires no charging time and allows for much quicker flash rates, but drastically reduces the lifetime of the flash tube if powered for significant periods of time. Such strobes require a form of current limiting, without which the flash tube would attempt to draw high currents from the electricity source, potentially tripping electrical breakers or causing voltage drops in the power supply line.
   BULLET::::- In both old and new designs, even mostly directly-coupled operational amplifier circuits, feedback through the power supply rails can generate ultrasonic oscillations that vary in amplitude at a low frequency (squegging) due to the power supply voltage sagging as oscillations build up (the long time constant coming from the power supply reservoir capacitor) in such a way that the low frequency is audible even though the high frequency fundamental is not. Such problems can be difficult to diagnose.
   BULLET::::- Auto dumping – the ability to partially discharge the light’s capacitors when the output power is reduced. Without this feature, when the light's output is turned down, it has to be fired to fully discharge the capacitors, then the capacitors recharged up to the new lower level.
  
  BULLET::::- Power recycle indicator - A light or sound emitter or both which tell the photographer that the flash has fired, and is currently charging.
   Despite being a relatively new member of the percussion family, steelpan tuning techniques have advanced rapidly. Strobe tuners are ideally suited for the task. The need to see the first few overtones further makes a strobe tuner a necessity for steelpan tuning. Steelpan makers have used strobe tuners since it was discovered that, by adjusting the overtones (first (fundamental), second, and third partial), the pan's sound seemed to sparkle in a way that it did not previously.
   BULLET::::- A common application for charge-pump circuits is in RS-232 level shifters, where they are used to derive positive and negative voltages (often +10 V and −10 V) from a single 5 V or 3 V power supply rail.
  
  BULLET::::- Charge pumps can also be used as LCD or white-LED drivers, generating high bias voltages from a single low-voltage supply, such as a battery.
   Flashing lamp strobes are also adapted for pop use, as a lighting effect for discotheques and night clubs where they give the impression of dancing in slow motion. The strobe rate of these devices is typically not very precise or very fast, because the entertainment application does not usually require a high degree of performance.
  
  Section::::Other effects.
   Companies such as Wheelock and Simplex discontinued their translucent strobes, and replaced them with new, clear, high-intensity strobes. Today, strobe synchronization is often used to synchronize all strobes in a uniform flash pattern. This is to prevent individuals with photosensitive epilepsy from potentially experiencing seizures due to unsynchronized strobes.
  
  Section::::Voice evacuation.
   A commonly used device requiring a trigger transformer are strobe lights. Strobe lights consist of a tube containing an inert gas, such as xenon. Capacitors inside the light are charged up to a relatively high voltage, roughly 300 Volts for small strobes. This voltage itself is not capable of ionizing the gas in the flash tube, and the tube will not fire. If the capacitors were charged to a voltage high enough to ionize the tube, the result would be no longer a flash, but a continuous arc as the voltage is sufficient to maintain ionization in the flash tube.
   Most strobe lights on sale to the public are factory-limited to about 10–12 Hz (10–12 flashes per second) in their internal oscillators, although externally triggered strobe lights will often flash as frequently as possible. Studies have shown that the majority of people that are susceptible to the strobing effects can have symptoms at 15 Hz-70 Hz, albeit rare. Other studies have shown epileptic symptoms at the 15 Hz rate with over 90 seconds of continuous staring at a strobe light. There have been no known seizures at or below the 8 Hz (or 8 flashes per second) level. Many fire alarms in schools, hospitals, stadiums, etc. strobe at a 1 Hz rate.
   Strobelights are often used in nightclubs and raves, and are available for home use for special effects or entertainment.
  
  Section::::History.
  
  The origin of strobe lighting dates to 1931, when Harold Eugene "Doc" Edgerton employed a flashing lamp to make an improved stroboscope for the study of moving objects, eventually resulting in dramatic photographs of objects such as bullets in flight.
   BULLET::::- Spark-excited or Spark Gap Tesla Coil (SGTC) - This type uses a spark gap to switch pulses of current through the primary, exciting oscillation in the transformer. This pulsed (disruptive) drive creates a pulsed high voltage output. Spark gaps have disadvantages due to the high primary currents they must handle. They produce a very loud noise while operating, noxious ozone gas, and high temperatures which often require a cooling system. The energy dissipated in the spark also reduces the Q factor and the output voltage.
   Once the main storage capacitor has finished charging, a smaller capacitor is discharged into the trigger transformers primary coil. A large magnetic pulse is generated inside the transformer, which is coupled to the secondary coil through the core. The secondary coil consists of hundreds, or even thousands of windings of very fine copper wire so a high voltage pulse is generated, in the order of 2-6 kV (2000-6000 V), depending on the length of the flash tube, and the gas contained within the tube. This high voltage pulse overcomes the resistance of the gas, and allows ionization.
   Section::::Strobe tuners.:How it works.:Strobe developments.
   In many two-stroke engines, the exhaust port is opened and closed directly by the position of the piston rather than by a separate valve, which restricts the timing of its operation; Typically, the port remains open long after is optimum, allowing some of the incoming charge to escape. This can be partly addressed by use of a tuned exhaust system to deliver a pulse of positive pressure prior to the port closing, to retain the charge.
  
  Section::::Two-stroke engines.:Alternatives.
   To observe the effect of back-EMF of a motor, one can perform this simple exercise. With an incandescent light on, cause a large motor such as a drill press, saw, air conditioner compressor, or vacuum cleaner to start. The light may dim briefly as the motor starts. When the armature is not turning (called locked rotor) there is no back-EMF and the motor's current draw is quite high. If the motor's starting current is high enough it will pull the line voltage down enough to notice the dimming of the light.
  
  Section::::See also.
  
  BULLET::::- Electromotive force
  
  Section::::External links.
   Strobe Edge
  
  Section::::Plot.
   Typical sound followers lock by using 240 Hz bi-phase interlocking pulse signals to sync sound to film. The 240 Hz bi-phase is ten times the 24-frame rate. Sound followers are found in many post-production studios for record and playback and in movie theater for sound playback. In use, the 24 frames per second is slowed to 23.976 frames/s to lock to SDTV and some HDTV standards, thus the digital bi-phase pulse is 239.76 Hz.
   In addition to photon shot noise, there can be additional shot noise from the dark leakage current in the image sensor; this noise is sometimes known as "dark shot noise" or "dark-current shot noise". Dark current is greatest at "hot pixels" within the image sensor. The variable dark charge of normal and hot pixels can be subtracted off (using "dark frame subtraction"), leaving only the shot noise, or random component, of the leakage. If dark-frame subtraction is not done, or if the exposure time is long enough that the hot pixel charge exceeds the linear charge capacity, the noise will be more than just shot noise, and hot pixels appear as salt-and-pepper noise.
   BULLET::::- Regular Audion Detector Bulbs are not adapted for the reception of continuous waves, because the vacuum is not correct for the purpose and because the filaments must be operated at such a high intensity that they give very short service, making them unnecessarily expensive.
  
  BULLET::::- Also page 44 stating,
  
  BULLET::::- BLUE DISCHARGE OF GLOW
   The trigger voltages provided by some modern flashes or radio triggers can also be too low to reliably trigger electronic circuits in the camera or receiver. Trigger circuit voltages below ca. 2 to 2.5 volts may exhibit this problem, unless the triggering circuit is specifically designed to work with such low voltages.
   BULLET::::- This appears in some Audion Bulbs and not in others. If allowed to persist, the vacuum automatically increases. For this reason the glow should not be allowed to appear and certainly not to continue, as the vacuum may rise to a very high value, requiring very high voltage in the “B” battery.
   BULLET::::- Glowplugs operating or wait to start (most diesel engines) – Appears when the engine is switched on to indicate the engine glow plugs are operating, and the driver should wait for the light to extinguish before starting the engine. Usually shaped like a coiled cord.
   BULLET::::- Static triggered spark gap - Commercial and industrial circuits often apply a DC voltage from a power supply to charge the capacitor, and use high voltage pulses generated by an oscillator applied to a triggering electrode to trigger the spark. This allows control of the spark rate and exciting voltage. Commercial spark gaps are often enclosed in an insulating gas atmosphere such as sulfur hexafluoride, reducing the length and thus the energy loss in the spark.
   Section::::Chorus Motors.:Motor types.
  
  The Chorus Meshcon motor is a high-phase-order motor/drive system that claims to offer up to ten times the "burst", start-up, or acceleration torque of a conventional motor and drive of the same rated power and base speed.
  