BIAS FX Mobile and two inputs



  • I've got a guitar with two jacks, one for the magnetic pickups and one for the piezo pickup.

    If I connect these separately to the two inputs on an audio interface (for example, the Focusrite Scarlett 2i2), and connect that to an iPad, will I be able to process each input separately in BIAS FX Mobile (separate amps and effects) and then mix them into a stereo output (lets say mag channel panned mostly to one side, piezo channel panned mostly to the other side)?

    Essentially the same as plugging in two guitars to the audio interface and processing each guitar separately in BIAS FX Mobile, and then mixing at the end.

    What kind of processing power would be necessary on the iPad to do this?

    For example, the following table shows benchmark results from Geekbench 5 for various iOS devices, with single-core CPU, multi-core CPU, and GPU numbers.

    0_1570222960971_Screenshot from 2019-10-04 14-01-37.png

    Which numbers should I care about? How much CPU or GPU power do I need to process two input channels?

    Thanks,

    Greg



  • For iPads, using the ARM CPU, I see that there are vector instructions (i.e. single instruction, multiple data) which would he helpful for DSP, which the ARM folks call NEON. There is even an open-source project called Ne10 to provide a library of common algorithms, including fast Fourier transforms typically used in DSP, using the NEON instructions, and supports iOS.

    PG developers, do you use the NEON CPU instructions on iOS?

    Apple's ARM processors (used in iPads) also have proprietary DSP instructions.

    PG developers, did you use Apple's DSP instructions in their A12 or A13 CPUs?

    Also, did you parallelize your code to run on multiple ARM CPU cores?

    The other option on iPads is to use Apple's GPU, which is embedded in the same chip as the CPU. You could use the OpenCL library to do this, which provides an implementation of FFT. You could also use Apple's Metal API.

    Did you use the GPU on the iPad?

    Thanks,

    Greg