Simplify the following text for a Grade 7 native English-speaking person.
Original: When first interviewed about this , the sound engineers claimed that they had used a vocoder ( although they did not specify that it was Auto-Tune , a phase vocoder ) , in what Sound on Sound perceived as an attempt to preserve a trade secret .
Simplified: At first the sound engineers claimed that they had used a vocoder , in what Sound on Sound said was an attempt to keep a trade secret .