“I have three synthesizer modules and one keyboard connected to a single port MIDI interface. I’m able to play the keyboard’s sounds and those of the modules through my sequencing software. I connect them all in a chain using the MIDI thru ports. A friend told me I’d be much better off with a multi port MIDI interface connecting one to each port. Is this true?”
There could be some benefits depending on what the synths are and/or how you are using them. Each time you connect a MIDI product to the MIDI thru of another you add a little bit of delay to the MIDI signal getting to that second unit. This latency is normally just a few milliseconds and hardly noticeable, but when you have three or four chained together the lag can become significant by the time it gets to the last instrument. This may or may not be a significant problem for you depending upon how you are using that last synth. Further, while the delay can be awkward when playing in real-time, you can offset the delay in your sequences by sliding those tracks forward in time a corresponding amount. Generally speaking the more critical the timing for a given set of data the better it is to devote a MIDI port to it.
If the synths have mulitimbral capabilities you’ll benefit from having them on separate MIDI ports, which will allow you separate MIDI control over each sound you are using. Still, you can sometimes combine two or more synths on one port. Let’s say you have two units that you’ll only use for eight MIDI parts each. You may be able to combine them on a single MIDI port, using one for MIDI channels 1-8, and the other on 9-16. There are some limitations to this in terms of global control (see below), but it’s often a workable solution nonetheless.
If you want to be able to do program dumps and other more in depth control of the instruments from your computer such as editing parameters, each one will have to have two way communication to the computer, which is normally accomplished by devoting a MIDI port to each. Additionally, some global parameters of equipment can be controlled through MIDI, and some of those require bi-directional communication. If you do not need to do this very often you may decide to get by with a smaller interface and temporarily repatch the synths for these operations.
One common misunderstanding relating to this subject pertains to system exclusive commands. Many users think each instrument must be connected to its own MIDI port for them to work. This is generally not the case. The whole idea of system exclusive commands is that the data is specifically coded for an individual brand and type of device. So long as only one of the specific model is connected to a given MIDI port most system exclusive commands will work fine, even when the data must pass through other makes and models along the way.