parallel master daw and tape

[kalony]

I had a live recording of a Johnny Cash tribute Band to mix and master. And for mastering I tried to use an Tascam 103 Casette Tape.
It was funny, but a lil too much, so I tried to make it parallel and to sync it with the original mix. But that didn’t worked.

I placed a 1-sample-long piece of audio in front, to have a good visualization to sync the tracks.
I played back the mix, send it to tape and immediately back into PT again so that the tape won’t have 2 different speeds while recording and than playing back afterwards. It was just 1 run. So I thought the deal would be only the technical latency and the time from the recording head to the playback head.

But I could not sync the tracks in pro tools. Every Time I was on point, I got a weird scratching of high frequencies. It was no chorus and no phasing like you get, when you come close to sync. To describe it, I think more of a Lesley effect in the upper frequencies….

is there anyone who tried something similar?

Am I doing something wrong?

Is my tape vary the speed just a lil bit so fast, that I can’t hear it in solo mode, but when I listen to mix and tape in parallel?

Cheers and Greetings

Thomas