While recording a dictation with a 52xx series SpeechMike, and a sound is heard through the SpeechMike speaker, thereafter the current dictation changes pitch or becomes garbled.
This can occur on the series II SpeechMikes (52xx models of Cassic and Pro) with installed firmware 1.20.
This is not an issue with series II barcode SpeechMikes because they do not use firmware 1.20
Upgrade the device firmware to 1.26. This allows for the SpeechMike to run in Full Duplex mode but restricts the recording and playback sampling frequency to 22Khz.
Download firmware wizard 1.26
Downgrade the device firmware to 1.18. This supports only Half Duplex mode but allows for the recording sampling frequency to be changeable.
Source: Philips Technical Team