I have an App on my phone called SoundHound. It is an App that you can open and it will listen to a 30 second clip of any song then tell you (using the internet) who the Artist and what the Name of the Song is.
Today I was listening to my Silver C100 and I always felt that the lower deck seemed to play a little slower than I would like but not enough to warrant pulling things apart again to adjust.
I was playing a store purchased cassette and decided to let the phone app listen in. To my surprise it came back with Not Found. What? It's only Hotel California by the Eagles....what do you mean you can't find it or know what it is? I tried again. No dice. Played it in the flat slot deck...picked up on it right away.
Come to find out your deck has to be playing the song at the EXACT CORRECT speed before the App will identify it. Figuring the store purchased cassette was most likely recorded at the correct speed I proceeded to take the back off of my box. I played the exact same song off the internet while matching the motor speed on the cassette for a perfect match to the digital version speed online. Wham! Now every tape I pop in it names the songs with only seconds of listening time. Guess I must've nailed the tape speed.
So I learned something today. It's an easy way to tell if your deck is in the ball park of correct speed on playback. If you have time you might try the App on your phone while playing a cassette. If it is able to pick up on your song it means your tape speed is in the ball park of perfect and while there are professional ways of adjusting the tape speed (as I found out today) this is an easy way to test your decks playback in a pinch.