Suggestion on suitable arm processor

https://emotiv.com/product-specs/Emotiv%20EPOC%20Specifications%202014.pdf

I've noticed that it's supposed to connect to a computer via USB 2.0, so it might be a good idea to get a microcontroller, which supports USB Host.

I also saw that for Android, it uses BlueTooth.

Since the computer is also doing FFT, I think the Cortex-M7 is the minimum requirement for such applications (though the Cortex-M4 might be able to do some of the things).

But looking further on the specs, the minimum requirements for a Windows/Mac/Linux computer is 2.4GHz.

That suggests that a Cortex-A would be a good choice; preferrably with multiple USB host ports.

As each USB2.0 port is 480 Mbit (280 Mbit effective data), the port is able to transfer a maximum of 35 MByte/sec.

A Cortex-M7 might be able to handle a single host port and do FFT on it, but maybe it's best to move up to a faster processor if you need to control more than a single target.

-I believe any Cortex-A7 and later would be able to do the job just fine for more than one USB connection.

This is a qualified guess only. You may want to contact emotiv and ask them how much data they transfer per second; let them know that you plan to interface to their device using a microcontroller / microprocessor.

Also ask them if they can provide information on how to communicate with their device via USB or BlueTooth (or both).

Note: Various boards are already available for a low cost. Some popular boards that can run Linux are:

Raspberry Pi 2 ($39), CubieBoard ($35), CubieBoard2 ($59) and CubieBoard3 ($70 - this is also called CubieTruck).

-But running Linux does not automatically mean that you can run the software, which emotiv supplies for Linux; it needs to be compiled for the processor you're using.

https://emotiv.com/product-specs/Emotiv%20EPOC%20Specifications%202014.pdf

I've noticed that it's supposed to connect to a computer via USB 2.0, so it might be a good idea to get a microcontroller, which supports USB Host.

I also saw that for Android, it uses BlueTooth.

Since the computer is also doing FFT, I think the Cortex-M7 is the minimum requirement for such applications (though the Cortex-M4 might be able to do some of the things).

But looking further on the specs, the minimum requirements for a Windows/Mac/Linux computer is 2.4GHz.

That suggests that a Cortex-A would be a good choice; preferrably with multiple USB host ports.

As each USB2.0 port is 480 Mbit (280 Mbit effective data), the port is able to transfer a maximum of 35 MByte/sec.

A Cortex-M7 might be able to handle a single host port and do FFT on it, but maybe it's best to move up to a faster processor if you need to control more than a single target.

-I believe any Cortex-A7 and later would be able to do the job just fine for more than one USB connection.

This is a qualified guess only. You may want to contact emotiv and ask them how much data they transfer per second; let them know that you plan to interface to their device using a microcontroller / microprocessor.

Also ask them if they can provide information on how to communicate with their device via USB or BlueTooth (or both).

Note: Various boards are already available for a low cost. Some popular boards that can run Linux are:

Raspberry Pi 2 ($39), CubieBoard ($35), CubieBoard2 ($59) and CubieBoard3 ($70 - this is also called CubieTruck).

-But running Linux does not automatically mean that you can run the software, which emotiv supplies for Linux; it needs to be compiled for the processor you're using.