Thank you all for your replies.
It may not be Aleksei's voice then. Well, it's a disappointing thought but I was anxious to hear what you experts would say
(well, the only experts I can easily approach anyway
)
It was a thrilling idea to have heard the tsarevich's voice and that alone has left an impression - even if it was a false one, it was worthwhile just to get that sensation.
Btw I found out that the audio recording is also used on a CD by folk singer Jeanne Bichevskaya called 'Tsar Nicholas'. I found this out after visiting the Frozen Tears website - I had seen the website's name but never actually visited it before. I was very pleased when I did. I have listened to the album also now and it's a very nice inspiration in the background while I am writing and researching for my collection of poems about Aleksej - I have about 30 now