I'm not sure about that particular device, but there's some pretty good info in the replies to this post:
https://midi.org/forum/9242-looking-for-some-sample-smpte-midi-files

And a bit more, but maybe not as relevant here:
https://midi.org/forum/1818-can-midi-beat-clock-be-printed-onto-a-smf

Thanks Jason for responding.

What I am really trying to find out is how frequencies are maintained when MIDI clocks slow or quicken a tempo.

For example, if I record from one tape machine to another through a MIDI sync box like the MIDIizer but slow the tempo using the inbuilt translator - let's say from five minutes of audio to ten, the receiving tape is slowed down but the audio frequencies are unaltered. Consequently, how is this achieved simply from MIDI clock pulses? Maybe there are pauses or breaks in the signal?

MIDI does not record frequencies like a tape, it records which notes to play.
If you play the same note it will have the same frequency whether you play it fast or slow.

Sema, I am analysing tapes containing speech. They do not contain musical notes. There are additionally silent pauses in between exchanges yet MIDI clock has slowed these also.

As with musical note, you don't control the tape speed, you control the playback start point.

Yes, I understand that. I was wrong to say the tape is slowed down, it just appears that way when, as in my example, five minutes of audio have now been fitted into ten minutes of actual tape space.

This is what I do not understand. If the audio has just been spread out there must have been gaps created in-between what was previously a continuous electronic signal. What is in these gaps - noise? Has the MIDI translator effectively turned the analogue signal into a digitized one?

For this particular device, this video explains a lot.
https://youtu.be/wfzgI-K0RuY
He has to record the timecode on to both tapes before doing any work with them.
As Sema noted, it is used to select the start point of playback, and also record.
The tapes run at the speed of the time code that is already recorded on them.
So it looks/sounds like you are just picking the playback and record start spots, and any actual audio gets recorded at standard speed.
I'm also now curious if it actually does allow time stretching. I have not delved in to the manual yet.

[quotePost id=18731]What I am really trying to find out is how frequencies are maintained when MIDI clocks slow or quicken a tempo.
For example, if I record from one tape machine to another through a MIDI sync box like the MIDIizer but slow the tempo using the inbuilt translator - let's say from five minutes of audio to ten, the receiving tape is slowed down but the audio frequencies are unaltered.[/quotePost][quotePost id=18733]I am analysing tapes containing speech. [...] There are additionally silent pauses in between exchanges yet MIDI clock has slowed these also.[/quotePost]
Can you explain more about how your speech tapes were created and how the equipment was connected? I have some doubts that the Tascam MIDIizer MTS-1000 and MIDI clocks were used to do the time expansion you are describing.

I can't find the manual for the Tascam MIDIizer MTS-1000 online to confirm exactly what it can do. However, my understanding is the MIDIizer can not "slow the tempo using the inbuilt translator - let's say from five minutes of audio to ten" and the recorded sound on the receiving tape can not be "slowed down but the audio frequencies are unaltered" -- at least not with a typical tape deck doing the playback.

In order to play an analog tape at a different speed and keep the pitch the same (or play at a different pitch and keep the speed the same), my understanding is you need a special kind of tape player with rotating heads. For example, see this blog post: Pitch Shifters, pre-digital. My understanding is the MIDIizer can not help preform this kind of analog tape time expansion or pitch shifting.

When a time code signal is recorded on a tape, I believe the goal is to be able to precisely locate specific positions in fractions of a second on the tape. When a tape deck is playing or recording it will always be advancing the tape's time code at the true speed -- the seconds indicated by the time code signal are never sped up or slowed down.

By editing a tempo map, the MIDIizer can slow or accelerate the audio playback and record. SMPTE to MIDI translators allow a given amount of time to be converted to a MIDI tempo, and vice versa. SMPTE is based on the 24hr clock and is broken down into frames and sub-frames, MIDI on the other hand is based on beats per minute (BPM). If a song (or in this case speech) is five minutes long that would equate to so many BPM or MIDI measures. If you then halve the number of measures by reducing the tempo by half, the five minutes becomes ten, and the length of the recorded song (or speech conversation) is doubled. As yourself, I cannot understand how this is achieved electronically without the pitch becoming altered.

(I have a MIDIizer MTS 1000 manual in pdf but unfortunately cannot upload it to the forum, as it is exceeds the 2MB file limit.)

[quotePost id=18747]I have a MIDIizer MTS 1000 manual in pdf but unfortunately cannot upload it to the forum, as it is exceeds the 2MB file limit.[/quotePost]
If you are on Windows, you can try using 7-Zip to compress the file into a multi-part zip file. You'll have to rename* the files to end with ".zip" because this forum only allows you to upload files with certain file name extensions. [See attached picture 1.]

People who want to download and combine the files will do the reverse steps: Rename* the zip files so they have the original extensions of 001 and so on. Right-click on the 001 file and open it in 7-Zip, then you'll see the original file in 7-Zip and can drag it somewhere to extract it. [See attached picture 2.]

* Before renaming the files, make sure Windows is showing filename extensions. In any folder, go to the View toolbar. In the section for Show/hide, make sure the checkbox "File name extensions" is checked. [See attached picture 3.] If there is no View toolbar in Windows 11, you may have to do the following: In any folder, click the ... icon and go to Options. In the Folder Options dialog box, go to the View tab, and make sure the checkbox for "Hide extensions for known file types" is unchecked. [See attached picture 4.]

Unfortunately this pdf file is already compressed to the maximum. I tried 7-Zip, Adobe and Winzip but to no avail.

Perhaps I can send it by personal mail, but I don't whether that is allowed by the forum rules.

[quotePost id=18749]this pdf file is already compressed to the maximum. [...] Perhaps I can send it by personal mail[/quotePost]
When you attach files to a post on this forum, you can upload multiple files. Each individual file must be 2 mebibytes or smaller, but the total size of all the files can larger.

To share a file larger than 2 mebibytes, my idea was to use 7-Zip to create a multi-part zip file. Even if the total size can't be reduced any further, this process will create multiple files that are each 2 mebibytes or smaller. (See attached picture 1 in my previous post for the 7-Zip setting circled in red to make files up to 2M in size.)

You can send it to my e-mail if you want, but I think other people reading this thread will want to look at it too. I was hoping that splitting the file into parts could help anyone reading the thread now or in the future have a look at it, although it might be a complicated workaround.

Sorry about that. It took me a while to work it out!

Here is the MIDIizer MTS 1000 manual split into two Adobe parts, compressed in Winzip.

Thank you for sharing the manual. After reading the manual, I still think the MIDIizer can not make large changes in the tape speed when a tape deck is playing or recording. I included a few relevant excerpts from the manual below.

If your tapes contain audio that has a different speed from the original audio source but the pitch stayed the same, then I think the MIDIizer was not the relevant part of this process. If you can describe how your tapes were created and how the equipment was connected, maybe we can better understand and answer your questions.

_______

Page 5 of the manual has a list of things the MIDIizer can do. It says you can

In other words, you can speed up or slow down the playback of a MIDI device, but speeding up or slowing down a tape deck is not mentioned.

In order to keep the tape running at the correct speed during playback or recording, the MIDIizer might make small adjustments to the tape speed, but this is just to keep the time code running at the true speed. It look like it's not able to make large speed changes (such as to reduce a 10 minute piece of audio to 5 minutes), and it seems it is not designed to keep the pitch of the audio on the tape the same while it changes the speed.

Page 10 of the manual includes the following description of the small speed changes:

After reading the following description on page 12 of the manual...

...that suggests that if the MIDIizer makes large changes in tape speed there would be a noticeable variation in the pitch of the audio.