These tools are known to work well in the latest desktop and mobile versions of Chrome, Brave, Firefox, Safari and Edge web browsers (which implement the Web Audio API and can be downloaded here). They may work, with some sound artefacts and some features disabled, in Internet Explorer 11 (where Flash is required).
However, if you are having strange problems with the sound, it's almost always worth trying a different web browser in case that helps.
You may find that sound can be heard through headphones but not through the speakers. If this is the case then:
Unfortunately you must make sure the screen stays on while using the tools that play sound. As soon as the screen turns off, all sound will stop.
There is no need to keep the screen on when using an Android device, unless you are also using the speech synthesis function (e.g. the "Say it" button setting). For some reason, if speech is enabled and the screen turns off then all sound will stop. The tools try to force the screen to stay on when speech synthesis is being used so if you notice that your screen is not turning off, then this is likely to be the cause.
Some people report that the initial "dit" is missing or an initial "dah" is played as a "dit". There are a couple of reasons:
In both cases, you may try adjusting the "start-up delay" in the "advanced timing" controls (present on most pages). This configures a delay put in between pressing the "Play" button and the first sound starting. The audio system is started when "Play" is pressed so it provides a chance for other parts to activate. If you are using Bluetooth headphones, the other option is of course to try wired headphones or the speaker.
The download button downloads a WAV file of the active sound with a pause at the end defined by the segment gap. Some versions of Safari do not properly support the download button but it can be made to work in the desktop version by holding the Option key when clicking it and then saving the file with the ".wav" file extension.
The choice of voices available for speech synthesis is determined by the combination of your web browser (e.g. Chrome, Firefox) and operating system (e.g. Windows, MacOS, Android). The software will try to choose a sensible default voice matching your local language setting. If you load a file with settings in and with a voice defined the voice in use may or may not be changed, depending if the one in the settings file matches one that you have available on your system.
Your web browser will cache a copy of each page you visit to reduce download time. This means that sometimes you will not see the latest version of one of the pages. The tools on the pages do not have version numbers, but normally the in-page "Change log" will indicate when there has been a new feature added along with the date so this can help. To get the latest version, you need to force your web browser to retrieve a fresh copy.