say they can curb dog barking by releasing a high- frequency whistle.

 Some apps, such as  say they can curb dog barking by releasing a high- frequency whistle.
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Hello ! Teach your dog new tricks with this simple to use dog whistle. Stop dogs from barking! Initiate a variety of frequency sounds. Set it on your main screen as widget. You can use it as anti dog repellent. Here’s App…

In the Dog Bark Deterrent mode, frequency is variable between about 4kHz and 20kHz.
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Stop barking with our newest, most powerful ultrasonic bark control device to date. Whether it's your dog or the neighbor's dog, the Dog Silencer will help you regain the peace and quiet that's been disrupted by nuisance barking. This revolutionary device automatically detects and stops barking with special sound frequencies and works up to “A dog can hear sounds in the ultrasonic range, which is at a much higher frequency than humans. An ultrasonic bark control device:
Photo provided by FlickrIn time, the dog will start to associate the barking with the waterspraying, so he will be less likely to bark as frequently as before.
Photo provided by FlickrI don't know what envelope analysis is. I can picture using a speaker or tranducer to sample the frequency of the dog's bark and then designing
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"Never has there been a more comprehensive and humane solution to Eliminating Dog Barking!" Every imaginable feature has been put into the all new Dog Silencer. This completely humane Bark Control has features never presented in bark control until now. Introducing the all new Sound Comp Technology™" which sweeps through a variety of frequencies to target the barking with the right frequency. There are some bark control products that do use sonic and ultrasonic technology but rarely do they use both all in one unit, and even when those units utilize ultrasonic technology it is done ineffectively with a conventional speaker. The Dog Silencer uses an all new sound generating component called a "high pressure transducer", which used in this type of application is a superior technology, so the sound output can carry further than any other unit currently available.Through testing, we found larger dogs tend to react to lower tones while smaller dogs tend to react to higher frequencies. When first using and testing the Dog Silencer Pro, we recommend setting the unit to sonic sound so you can hear the frequencies turn on when the dog barks. Once you’ve set the Dog Silencer Pro to your desired sensitivity level, you can switch the frequency back to ultrasonic.If you have a dog that keeps you up at night, gets you in trouble with your neighbors or you are just tired of hearing all of the time, then BarkWise is what you need. NOT just another Dog Collar, BarkWise emits a high frequency sound pulse in direct response to your dog's barking. The powerful sound is inaudible to humans yet disrupts the barking patterns of your dog without causing pain or injury to your pet. BarkWise doesn't use Electric Shocks to control behavior, rather it uses the high pitched sounds to train your dog not to bark. These sounds interrupt the barking without hurting your dog. The dog will usually learn quickly to associate barking with the unpleasant sound, and this will reduce or completely eliminate "nuisance" barking. BarkWise is a pet friendly, safe and effective way to train your pet.Dogs can hear a greater range of sounds than people can. People hear sounds in the frequency range of 64 to 23,000 hertz while dogs can hear sounds in the frequency range of 67 to 45,000 hertz. According to dog behaviorist Steven Lindsay, frequencies above 36,000 hertz can be painful to dogs, resulting in whining or barking. These sounds are inaudible to people but are used in personal dog deterrents to startle dogs and make them want to get away from the noise.