So what you're attempting to do, is restore the pitch (i.e. "speed") of the recording. The reason it didn't work is that you used a timestretching algorithm instead, which leads to an unwanted outcome.
Some bits on timestretching...
Generally, the difference is, timestretching and pitchshifting uses an algorithm to effectively adjust only one parameter.
Timestretching adjusts the duration and not the pitch.
Pitchshifting adjusts the pitch (or frequency) and not the duration.
Different software may use different names for them, but, under the hood, they both use the same or similar algorithms, and none are perfect. You always get artefacts that the trained ear may notice, especially if it's a big adjustment or a real-time algorithm.
Pitch adjustment!
So what you needed was simple pitch adjustment. For tape, you could have just slowed the tape movement, this would have been an ideal solution, if possible. In the digital domain it's more simple but less technically ideal; you just slow the sample clock/decrease the sample rate, so that a given duration becomes longer and so the pitch lowers (Imagine the samples as evenly-spaced dots along the length of the tape if it makes it easier to imagine that slowing the sample clock = slowing the speed). But then you need to resample back to the original sample rate (So that it plays back at the adjusted speed) to finalise the process (In the analogy, we would add new dots at the originally-timed spacing, independent of tape speed). This is what the process you should have chosen does, "resample", and also, this is why it's important to use high quality audio files for processing(!!).
How to do it correctly in Adobe Audition...
First, the Pitch Shift process is for adjusting musical pitch, and it does not adjust the pitch and time together - it uses an algorithm to adjust only the pitch so don't use it. Instead, if you use
Effects > Time and Pitch > Stretch and Pitch,
you will see an option to RESAMPLE, and if you absorbed what I said in the last section, you should realise what this mean - It's the same as slowing or speeding up the tape, but in the digital domain. It removes the independent pitch/time algorithm. You should turn all other settings off and just use the semitone or percent slider.
So that a 50% reduction in length/12 Semitone raise in pitch on a 440 Hz pure tone looks like this:
(The processed wave is on the bottom)
As you can see, the 440 Hz tone gets resampled to 880 Hz and so the duration is halved. No other processing is done - just a simple resample.
A 200%/-12 semitone adjustment (as we're doubling the duration/halving the frequency) looks like this:
As you can see here, the Pitch Shift process (Effects > Time and Pitch > Pitch Shift) only adjusts the pitch. The duration remains the same:
So DO NOT use Pitch Shift or any other independent stretching algorithm to restore the pitch on this occasion, as you want the TIME to adjust, too. So adjusting the speed through RESAMPLING is the way to go.
Note:
The spaces in pitchshifting and timestretching are removed so that you know it's a specific process or effect, not a general description. As pitch shift could mean speeding up or slowing down the sound to specific intervals of frequency, i.e. musical pitch adjustment. Also, I didn't explain the pitch/frequency difference and, further, I should have used "frequency" on some occasions, but as this is a beginner, I didn't want to confuse things further, so I detracted from some technical terms.
