Hi Stefan (heisst das, dass Du aus dem Deutschsprachigen Raum schreibst?)
First, a quick clarification on terminology.
Word Clock: This keeps all the ones and zeros in a digital audio stream aligned, so they don't crash into each other, causing pops and clicks (this is a simplified explanation... they don't literally "crash" into each other). It basically makes sure, that all the 44100 Samples that are transferred every second, are sent and received at the same time on the sending and the receiving end. Without this, audio would not sound "clean", but have clicks and pops everywhere.
Word Clock has NOTHING to do with two devices playing through a song in unison. That's what the next sync format is for.
SMPTE: This is a synchronization protocol that makes two (or more) devices play through a song in sync. It keeps their play position in the same spot (...also a simplified explanation, as there's some more details that regulate specific things that are needed to keep two or more devices playing/recording together almost like a single device).
SMPTE existed before MIDI, and can exist as an Audio Stream. However, on most "newer" devices with MIDI, a SMPTE signal is sent over MIDI, to keep two devices running alongside.
MIDI (Beat) Clock and MIDI Time Code (MTC): The purpose of this is similar to SMPTE above, but it's a simpler protocol that only works with MIDI-enabled devices (e.g. you can't sync an analog tape machine by striping one channel with an MTC signal... you have to use SMPTE for that). So, if all devices support MIDI clock or MIDI Time Code, then it's fine to use that. Between MIDI Clock and MTC, MTC is better and "almost" like "SMPTE via MIDI", but still a separate sync protocol. Midi Clock, is kind of just like a pulse or a metronome that keeps the beat. MTC sends a more detailed sync signal that can be configured to be nearly sample-accurate (i.e. exact position identifiers with beats and frames, etc.).
SMPTE is still superior and/or more full-featured because it's compatible with a wider variety of devices (e.g. it can be used with old analog gear that needs to sync).
So, you need to configure a "sync play-cursor position" protocol like SMPTE/MTC/MIDI-Clock to have two or more devices play hand-in-hand together and move through the same song at the same speed, going through the same song position at the same time, etc.
...and you need to get the Word Clock sync right, so that things don't click and crackle when using digital connections.
I never used an Alesis HD24, but did a quick Google Search and found this:
https://www.manualslib.com/manual/20745 ... ml?page=68Looks like, the HD24 does NOT generate SMPTE and can't read/interpret the SMPTE synchronization protocol, either. It looks like it can generate MTC, though.
The D8B cannot generate any of the above mentioned sync signals itself (except for Word Clock, if an Apogee Clock card is installed. If not, and only the stock clock card is installed, then it can only generate Word Clock for itself but not for any other devices... well... unless such other devices don't need to sync via a dedicated W/C connector, but are fine with using the W/C signal that is part of a digital audio transmission, such as via ADAT optical or S/PDIF).
You absolutely need MTC or SMPTE sync via MIDI, though, in order to get your D8B and HD24 to run in alongside, and sync their song playback/recording.
Since the D8B can't be the MTC generator, you have to configure your HD24 to send out the MTC signal to the D8B. How to do this on the HD24 happens to be described in the link I shared above. On the D8B, it's on the Setup/MIDI screen, but there isn't really much to configure and it should just generally chase the incoming sync signal, if a proper signal is received on the MIDI in.
The wiring you described sounds about right, when it comes to MIDI. If the W/C out was connected to lower BNC connector on an Apogee Clock card, and to the W/C in on the HD24, then this sounds about right, too. It won't work if the BNC word clock cable is connected to one of the Tape In/Out cards (e.g. DIO 8). Still not sure what those BNC connectors are even good for on these cards.
Long story short, there's different types of "sync". As for MTC sync, the HD24 needs to generate it, and send it to the D8B.
For Word Clock sync, the best setup depends on if you have the stock clock card, or the Apogee Clock Card in your D8B. What you're describing above ddn't make this very clear.
Hopefully this gives you a few pointers that you can play with. If it doesn't solve it, please get back with more specifics about the Clock Card you use (i.e. the card in the SYNC Slot. Is there a card with two BNC connectors in there, but no other connectors? Or is there a metal cover and you don't see a card?), and what connectors on it you use between the D8B and HD24.
Best of luck!
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Stefan just happens to be a common name in Germany, which is where I'm originally from. That's why I thought I'd ask 
