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Olympus OM-D whirring noise

Amin

Active member
I can hear the sound, but it doesn't bother me in the least.

As for the cause, I had an interesting email discussion about this with someone who would rather not be identified:

Have you noticed how the sensor jumps into position when the power is turned on? This means that the magnetic suspension must be on at all times for the sensor to be in the correct position!

This does not mean that IS is always on. The magnetic suspension is always on. By default, IS is OFF, which means that the sensor is stationary with respect to the camera body. In other words: no effort is made to cancel camera motion. No vibration dampening is occurring. No action is performed, other than maintaining the sensor in the correct position respective to the lens!

When IS is turned ON, then the vibration information provided by solid-state accelerometers is used to compensate for vibration. In other words: with IS ON, the sensor moves with respect to the camera body, in a fashion that (hopefully) cancels out vibrations.

The sound produced by one E-M5 may vary from the sound produced by another E-M5. The sound is the result of magnetostriction. The sum of the magnetic forces produced by the small windings in the IS assembly causes equivalent stresses on the windings themselves, causing them to vibrate. This is the same phenomenon that makes power transformers (like wall warts) hum, only the frequency is higher in this case. Since no two of these very small windings are exactly alike, their acoustic properties will vary slightly from one camera to the next. This is absolutely normal.

This is not something to be addressed by a firmware update. The magnetic suspension is required for the camera to operate properly. There is nothing wrong with the camera.
Any guesses as to why the sound is much quieter in video mode?

IS turns ON when video starts!

Magnetostriction is a bit of an odd phenomenon. To picture what's happening, think of a winding traversed by an electrical current. Whenever the current increases, the magnetic field pushing apart the individual strands in the winding increases, effectively minutely increasing the volume of the winding. When the current subsides, so does this mechanical force, allowing the winding to return to its relaxed state.

Now, the reason why there is a such high-frequency current variation in the said windings is related to electrical efficiency issues (preservation of precious battery power). A detailed explanation would be way beyond what seems appropriate here, so I'll simply suggest that you research the following topics if you want to dig further: Linear vs. Switched Mode Power Supplies, and Pulse-Width Modulation. Suffice it to say that it is more efficient to send a pulse train with a 50% duty cycle (50% of the time full ON, 50% of the time OFF) than to create a 50% amplitude constant current to drive a winding. The former uses less than half the power required for the latter, generally speaking, and the end result is identical.

So, the question is thus: we have tiny windings being fed high-frequency pulse trains. A corresponding vibration in the windings produces an audible sound in some cases and not others. Why? As it has been pointed out, the sound is, in the worst cases, really faint. I posit that the only reason it can be heard at all is because, when IS is OFF, the magnetostriction frequency is absolutely constant, and so is the resulting sound. When IS turns ON, the duty cycle (and/or frequency of the pulse train, depending on the strategy adopted by the designers) starts varying with the vibrations imparted on the camera (i.e. the IS goes to work). The faint sound is still there, but it is much harder to isolate because it varies constantly and randomly. In other words, it is much easier to train one's ear to a constant sound than to chase some ever-changing elusive whisper. There may also be some other electrical explanation (for example, a severe increase in pulse frequency when IS kicks in, moving the sound into the ultrasonic domain), but that would need to be verified in-circuit.

One could also speculate that there might be a resonance effect at work, effectively increasing the sound output when the frequency is constant and near a certain resonant frequency. But that would be pure speculation until resonance can be identified and demonstrated factually (and I would like to believe that such resonance would have been caught and eliminated by Olympus' engineers).
Is this all speculation, or do you have a reliable source at Olympus?

Is speculation backed by an entire career spent designing similar systems. I wouldn't say so. Actually, when I speak of the IBIS assembly as being the source of the sound, it is indeed a bit of speculation (I haven't yet put my hands on an E-M5). I point to the IBIS because it is the most likely culprit, and also because of some indirect clues (some people are reporting that what they hear clearly seems to be coming from the sensor area).

But the sound could very well originate from the switched-mode power supply (SMPS) of the camera, which uses inductors to translate the battery voltage to whatever regulated voltages are required by the circuitry. Such circuits are well-known for producing all kinds of buzzing/humming/whirring sounds. Think of laptop power supplies, _fancy_ LED flashlights, compact fluorescent lamp ballasts, etc. The explanation is exactly the same, as the inductors (=windings) used in SMPS circuits are subject to the same type of mechanical stresses as the IBIS windings are. Also, the sound would vary according to the power consumption, possibly explaining why the sound changes while recording video (although the buzzing from an SMPS usually gets louder with an increase in power consumption).

One way to find out would be to listen closely to the source of the sound. It is quite certain that the SMPS is located as far away from the sensor as it was feasible, most likely on the battery side. SMPS circuits tend to radiate significant electrical noise, and that's why you wouldn't want that anywhere near the sensor.

Anyway, same conclusion: all is normal, and it's hardware, not software. Perhaps refining some power consumption strategies could change the noise level a bit, but I doubt it very much.
 

ustein

Contributing Editor
> with mine it doesn't happen with the 12-50 kit . .

Strange as it happens with our 12-50mm.
 
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