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Audio-IO

Introduction

Assuming you are using a Digital Audio Workstation (DAW) instead of an all analog hardware studio, wideband audio I/O hardware is necessary to convert the analog signals from instruments and mics into digital bit-streams for computer processing, recording to hard drive and for re-conversion back to analog signals for play-back through headphones and speakers. All of which MUST be accomplished 1) in real-time (without latency), 2) with sufficient resolution, 3) with additional audio effects processing and 3) from/to many tracks (at least 8 and often 24 and more) all in parallel. This requires as much computing power and signal bandwidth as you can afford; although if all you need is 4 tracks in a portable system, a high-end laptop can provide sufficient services. However, even for this Very Small Studio, 24 tracks at 96 kHz 24bit with zero latency is not an unreasonable expectation. The problem is that despite the advertising and the fact that others have done it, the task remains non-trivial because of the technical details.

Disclaimer: This page is exclusive to the Presonus products in a PC-centric configuration but the digital concepts and requirements should apply to may other configurations.

PreSonus FireStudio Project Audio I/O

There are many digital-audio I/O boxes to chose from, but having chosen Studio One 2 from Presonus it was logical to also choose one of their FireStudio interfaces because of expected comparability. However, it is best not to lose sight of what the computer is being asked to do -- handle 24 tracks of 96 kHz sample rate 24bit bi-directional audio with zero latency in real time. (Rough mental calculation: 24 x 96x10^3 x 24 x 2 is over 110 MB/Sec assuming no processing, no data transmission overhead and no other computing tasks over an S400 [400 MB/s] 1394a [Firewire] interface. So, while Presonus has tested their products, user systems can vary, adding compatibility issues.

One notable headache has been lack of, or unstable, 1394 data sync -- the notorious "Red Light" problem. Lack of sync as well as unstable sync had plagued my studio for some time. Attempting to add a second FireStudio Project (FSP) unit was the final straw which, fortunately, lead to the solution. While the "cure" involved several factors, they had one issue in common; the need for data transmission bandwidth. Even with an S400 bus, anything which interferes with that resource can become a serious issue for getting the digitized audio in and out of the hardware.

Red Light Sync Solution
  • WinXP SP3 is insufficient and so not compatible with Studio One 2 and the FSP S400 data rates
  • Win7 Pro SP1 is a solid option for the PC; once it is configured properly
  • For the PC, 3 GHz, 4GB hardware, dedicated to studio use, appears to be a minimum configuration
  • A separate 1394 card appears to be required (not just a motherboard interface) with an approved chipset
  • Combined S400 / S800 1394 cards are NOT compatible even if the chipsets are approved
  • The only 1394 compatible card for PCI I found was the SIIG 3-port 1394a S400 NN-440012-S8
  • The Win7 default 1394 drivers do work and are preferred over any 3rd party drivers
  • The Win7 OHCI (Legacy) driver is actually faster and has better compatibility with the TI chipset
  • The 1394 card MUST be on it's own IRQ if at all possible -- do NOT share the IRQ with video or audio services
  • My PCI 1394 shared IRQ18 with a USB bus (unused) so I disabled that USB service
  • Wireless services demand higher IRQ priority in Windows so MUST be disabled (during studio I/O use)
  • The 1394 standard allows cable lengths up to 4.5 meters -- but the FSPs are only guaranteed with 4-6 ft
  • For longer runs from computer to FSP, use a UniBrain FireRepeater S400 with external power supply
Daisy-Chain FSPs
  • I have two (2) FSPs daisy-chained sync'd at 96 kHz, 24bit zero latency out 15 ft on a repeater
  • I used the UniversalControl Vers 1.7.2 to configure the devices
  • Configuration is simpler than it looks, but there are a few steps
    • Using S400 1394, there is no inherent need for using the SPDIF in/out lines
    • The FSP 1394 ports are labeled '1' and '2' but the order of use doesn't actually matter
    • For simplicity, just use port '1' as 'input' and poet '2' as output
    • Install the UC app, open and view the 'control window'
    • Configure each FSP independently:
      • Connect ONLY one FSP (lower S/N unit first), power-up and wait for the 'blue' sync
      • Look to see the UC recognizes the FSP; it will be listed at the bottom of the UC window
      • Click on the FSP 'box' at the bottom to show or hide the mixer window
      • Click 'Settings' and then 'Check Firmware'
      • If firmware update is required, do so now.
      • The FSP name field can be edited -- change it to 'FSP-1' or similar (use 'FSP-2' for the 2nd unit)
      • Click on 'FSP-X' unit to bring up the mixer
      • Click output '1/2' to switch it off to keep all output channels independent of each other
      • Change the sample rate to 96 kHz (or your own option)
      • Set the clock source to 'FSP-X Master' (which means using the FSP internal clock)
      • Set the 'operating mode' to 'zero latency'
      • Set the 'buffer size' to 1024
      • Each setting is remembered as it is changed so there is no 'Save' button
      • Power off the FSP interface - config is done.
    • Daisy-chain the FSPs once they have been configured
  • If using a DAW, not the UC, you don't need the UC interface available
    • In the UC app window, click Settings then UnSet the 'Run at startup' for the UC app
Multiple FSP Power-Up
  • At this point the system is more forgiving but there is is preferred power-up sequence
    • Power-up the computer and monitor
    • Power-up the S400 bus cable repeater (if you use one)
    • Wait for boot-up to complete and disable your wireless network card (if you have one)
    • Power-up the FIRST FSP in the chain -- and wait for a solid-blue sync
    • Power-up the SECOND FSP in the chain -- and wait for a solid-blue sync
    • Start the DAW
    • Reverse this sequence for power-down (though this is much less important)
  • Start StudioOne 2 and open the I/O config screen for mapping FSP Inputs and Outputs
  • Assign mono and stereo I/O which matches your hardware configuration