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The common claim is that the quality of traditional telephony is sufficient for the application and that every other solution offering more quality is probably just a marketing ploy. Imagine this situation:

Someone from tech support finally called our office via phone for the device in the server room that was beeping really loud. The caller said he couldn't hear anything beeping on his end. The device is quiet again, but how can this be? Some hotlines play music when they put you on hold, so this is hard to believe.


This happened to me and I was the one who called the office to analyse whats going on with the UPS that showed up in our monitoring.

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    Cellphone or traditional landline (copper line, not IP) phone on either end? Plain old telephone service has a limited freq. response. Also of interest might be Analog Telephone Frequency Response Curve. Really this is an electronics question, unless there was a claim that you should have heard the beep. – user3169 Mar 26 '15 at 21:17
  • @user3169 We and our customers use VoIP. Also I was actually the guy calling and not hearing the device, we noted the error codes on the display of the device, I checked the manual again and it states that the device also emits a permanent alarm when it displays the particular error code. If possible move the question to an SE site that is more appropriate. – LiveWireBT Mar 26 '15 at 21:28
  • I would ask your ISP if their system retricts frequency response. Probably they do because it reduces bandwidth. Sorry I do not have enough rep here to migrate, maybe someone else can consider it. – user3169 Mar 26 '15 at 22:02
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Yes, there are sounds that cannot be heard through the phone. Despite audible artefacts we usually forget that traditional solutions used in telephony have clear limitations, which may be why the caller struggled to come up with a good explanation why he wasn't hearing anything.

While you are able to listen to the remains of normal music or use a whistle, the system may be unable to transmit the beeping of a Piezo tweeter usually used in non-HiFi electronics to emit alarms.

No matter how loud the tweeter is, if the frequency is beyond the capabilities of a standard codec like G.711, you won't hear it.

This is a rare case where it's not about perceived quality, but a completely missing signal.

You can experiment with a program like Audacity to generate a frequency sweep, to test your hearing or certain codecs and devices.

Warning: Be careful with this, start with very low volume and consider that your neighbours might not enjoy it.

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