Managing DSP Resources

This article provides an overview of UA Audio Interface DSP and how you can tune the system to maximize available resources for UAD plug-in processing.

About Apollo/Arrow UAD Plug-In Processing

When operating UA audio interfaces, it helps to understand that UAD plug-ins within Console use DSP differently than when UAD plug-ins are used within a DAW. The most important differences are:

• In Console, you get Realtime UAD Processing and near-zero input latency when monitoring and tracking through UAD plug-ins, but all plug-ins on a single channel input strip must fit on one DSP core (or two cores if Channel DSP Pairing is enabled).
• In the DAW, you get DSP-accelerated processing for mixing with UAD plug-ins, but all plug-ins used in a DAW (not just UAD plug-ins) are subject to input latency induced by the DAW’s hardware I/O buffering (larger buffer size = more latency).

About UAD DSP Controls

Five settings are available within the UAD-2/Apollo/Arrow system that impact UAD DSP resources:

• Channel DSP Pairing, Cue Bus Count, and Input Delay Compensation are within Console Settings and apply to Apollo/Arrow only.
• DSP LoadLock and Limit DSP Load are within the UAD Meter & Control Panel application and apply to all UAD-2 devices in the system (including Apollo/Arrow and UAD-2 DSP Accelerators).
• These five settings are outlined below.

Channel DSP Pairing

Note: Channel DSP Pairing is available with UAD v9.10 and higher only (download now).

Setting location: Console Settings > Hardware Panel > Options Column

Tip: Lower the VIRTUAL CHANNELS value to conserve Apollo DSP.

Watch our UAD Basics video to learn about Channel DSP Pairing

Channel DSP Pairing increases Apollo’s DSP flexibility and lets you build bigger plug-in chains on Console inputs. As the DSP PAIRS value is increased, the VIRTUAL CHANNELS value is decreased. This reciprocal action lets you adjust how Apollo’s internal DSP resources are allocated.

Channel DSP Pairing control in Console Settings

Important: To maintain the lowest possible input latency for Realtime UAD Processing, UAD plug-ins on a single Console input channel strip must fit on one DSP core (or two cores if Channel DSP Pairing is enabled). This is why the “DSP resources were exceeded” message can appear when stacking DSP-intensive UAD plug-ins within a channel input strip, even if the UAD meters indicate DSP resources are still available. 

Channel DSP Pairing allows multiple UAD plug-ins that are inserted in a single Console input channel strip to span across two paired DSP cores. This feature effectively doubles the amount of Realtime UAD Processing DSP that is available on a single Apollo input.

Channel DSP Pairing lets you build bigger plug-in chains on Console inputs

When enabled (the default setting), Channel DSP Pairing is automatic. Simply insert UAD plug-ins in Console inputs as usual, and input DSP resources are automatically distributed across DSP pairs as efficiently as possible.

Channel DSP Pairing Notes

• Channel DSP Pairing changes the way available DSP resources are allocated. The feature does not increase the total amount of available DSP. 
• Individual UAD plug-ins must fit on a single DSP core, even when Channel DSP Pairing is available. A single UAD plug-in cannot span across paired DSPs. 
• Channel DSP Pairing values are saved within individual Console sessions files. Unlike other Console hardware settings, it’s not a global setting.
• Channel DSP Pairing applies to internal DSP within Apollo audio interfaces only. It does not apply to UAD-2 DSP Accelerators.
• Channel DSP pairing is unrelated to UAD plug-ins inserted in the DAW, where UAD plug‑ins automatically load on any available DSP.
• In multi-unit configurations, each Apollo unit has its own Channel DSP Pairing setting, and DSP can only be paired within an individual unit.
• Channel DSP Pairing is unavailable with Apollo Solo, Arrow, Apollo Twin SOLO, or Apollo models connected to the computer with FireWire.
• Channel DSP pairing is unavailable on Auxiliary and Talkback channels, nor at sample rates of 176.4 and 192 kHz.
• For complete details and specific examples, see the Console Settings>Hardware Panel>Options Column section within the Apollo Software Manual.

Input Delay Compensation

Setting location: Console Settings > Hardware Panel

Tip: Disable Input Delay Compensation to conserve Apollo DSP and reduce input latency.

Input Delay Compensation maintains phase alignment across Apollo’s inputs when:

1. Multiple inputs are used on a single source (such as when using two microphones on an acoustic guitar), AND
2. UAD plug-ins with additional latency are used on one or more of those inputs. 

If you don’t need Input Delay Compensation (if you’re not monitoring or recording Apollo inputs with BOTH of the above conditions), the feature can be disabled and input signals will remain phase aligned. A list of which UAD plug-ins have additional latency is in the Appendix near the end of the UAD Plug‑ins Manual. 

Important: Console’s Input Delay Compensation is unrelated to delay compensation in the DAW. The DAW’s delay compensation feature should always remain ON with UAD systems.

Set Input Delay Compensation to OFF when not needed

For more details about Input Delay Compensation, see the “Latency & Apollo” chapter within the Apollo Software Manual, or the “Latency & Arrow” chapter within the Arrow Manual.

Cue Bus Count

Setting location: Console Settings > Hardware Panel

Tip: Reduce the CUE BUS COUNT value to conserve Apollo DSP.

Apollo’s cue mix buses use DSP for signal routing and mixing. If you’re not using more than two cue buses (the default value), keep this setting at its minimum value of 2 to reduce DSP use.

Note: The Cue Bus Count setting is available on Apollo rackmount models only.

Reduce the CUE BUS COUNT if not using 3 or 4 cue mixes

DSP LoadLock

Setting location: UAD Meter & Control Panel > Configuration Panel

Tip: Keeping DSP LoadLock enabled is generally recommended for ease of use. However, depending on the plug-in and which of its features are active, disabling DSP LoadLock can conserve DSP.

DSP LoadLock reserves the maximum DSP load required by each UAD plug-in, even if certain features within the plug-in are unused (for example, disabling an EQ module within a Unison preamp plug-in). Enabling DSP LoadLock ensures there will always be enough DSP allocated in case those unused features are later enabled.

Note: Although disabling LoadLock increases available DSP by not pre-allocating DSP for unused UAD plug-in features, it may cause DSP resources to be exceeded when automating UAD plug-in parameters that affect DSP loads.

UAD plug-ins that conserve DSP when its features are disabled (and if DSP LoadLock is disabled) are marked with an asterisk (*) in the UAD-2 DSP Chart.

Limit DSP Load and DSP LoadLock settings

Limit DSP Load

Setting location: UAD Meter & Control Panel > Configuration Panel

Tip: Keep this setting at 100% during normal operation.

To maximize DSP availability and for optimum performance, keep the Limit DSP Load setting at 100% (the default value) unless a lower value is specifically recommended by UA customer support.

Monitoring DSP Resources

UAD DSP resources can be monitored with the DSP/PGM/MEM meters at the bottom of the main Console window or the main UAD Meter & Control Panel application window (these meters are mirrored in the two applications). Note that these meters display the global average of all DSP cores in the system.

Global system resource gauges in UAD Meter

For more precise resource availability, visit the System Information panel within the UAD Meter & Control Panel app. This view displays detailed loads on each individual DSP core.

Individual DSP core loads in UAD Meter>System Information panel

Additional UAD DSP Notes

• UA Audio Interfaces use DSP resources for internal DSP mixing and routing functions. Therefore, the UAD Meters show DSP and memory usage when Apollo/Arrow is connected, even if UAD plug-ins are not currently loaded in Console or the DAW, and/or if the Console application is closed.
• Depending on the UAD plug-in, lower session sample rates may use less UAD plug-in DSP resources than higher sample rates. 
• The UAD-2 DSP Chart shows how much of a single DSP core that individual UAD plug-ins use at 44.1 kHz. The chart can help you manage session plug-in choices.