Resolution ≠ Smoothing — Don't confuse them
This section concerns DSPs using DSP PC-Tool (Helix, BRAX, MATCH). miniDSP users should refer to the miniDSP Plugin documentation.
The Helix RTA in DSP PC-Tool has TWO independent settings that affect the display. Confusing them is the most common beginner mistake.
RESOLUTION (frequency step):
Controls the number of frequency bands displayed. The finer the resolution, the more detail you see.
- • 1/3 octave = 31 bands (ATF default — 'very practical because it reflects the human hearing impression very well')
- • 1/6 octave = 62 bands (recommended for Level Matching and TuneEQ — 'useful for detecting narrow-band flaws')
- • 1/12 octave = 124 bands (high detail, Individual Driver EQ)
- • 1/24 octave = 248 bands (maximum detail, rarely needed)
SMOOTHING (temporal):
Controls how fast the curve stabilizes. Does NOT affect the number of bands.
- • Fast = responsive but jumpy, less accurate in the bass
- • Normal = ATF-recommended trade-off ('the default value normal should be the best choice in most cases')
- • Slow = more accurate especially below 200 Hz, but longer stabilization time
Which setting for which task
Each measurement task has an optimal setting. Use the SAME setting for all measurements within a single session.
| Task | Resolution | Smoothing | Why |
|---|---|---|---|
| ISA (OEM signal analysis) | 1/3 oct. | Normal | Overview of the factory signal, no need for fine detail |
| Level Matching (Phase 11bis) | 1/6 oct. | Normal or Slow | Detect imbalances between channels — ATF recommends 1/6 |
| TuneEQ 2.0 (Phase 12) | 1/6 oct. | Normal | TuneEQ requires 'at least 1/6 octave resolution' (ATF release notes) |
| Start Analyzer (visual only) | 1/3 oct. | Normal | Global overview is enough, no corrective action |
| Individual driver diagnostic | 1/12 oct. | Slow | Isolate the narrow resonances of a specific driver |
Common pitfalls
- • Changing the resolution BETWEEN TuneEQ measurements → the corrections are no longer consistent. Keep 1/6 from start to finish.
- • Using 1/24 octave for Level Matching → too much detail, you correct noise instead of trends.
- • Confusing REW smoothing (visual post-processing) with Helix RTA smoothing (real-time measurement parameter). REW smoothing is a visualization tool applied AFTER capture. Helix RTA smoothing affects the CAPTURE itself.
- • Forgetting that the Helix RTA is a measurement tool INTERNAL to the DSP (it measures the signal AFTER DSP processing), not an acoustic measurement tool. For acoustic measurement, you need an external mic (UMIK-1, AMI, etc.) connected to the DSP.
Sources
- • ATF Knowledge Base RTA (audiotec-fischer.de/en/knowledge-base/DSP-PC-Tool/rta/) — sections 2.2 (Resolution) and 2.4 (Smoothing)
- • ATF Knowledge Base EQ — smoothing recommendations by task
- • ATF DSP PC-Tool 5 release notes — TuneEQ '1/6 octave resolution' requirement
- • ATF TuneEQ Setup screenshot — 'We would recommend adopting all settings as shown' (Resolution = 1/6 oct.)
Conclusion
Remember: Resolution controls how many frequency bands you see, Smoothing controls how quickly the display stabilizes. Pick the right combination for your task, keep it consistent within a session, and never confuse Helix RTA smoothing (measurement parameter) with REW smoothing (visualization post-processing).
Sound Architect
Sound Architect tells you exactly which RTA settings to use at each calibration phase.
Related Guides
Which Smoothing Setting Per Driver Type — REW Guide
Different drivers need different smoothing settings in REW. Using the wrong one leads to over-correction or missed problems. Here is the definitive guide.
REW Auto-EQ for DSP Tuning: Complete Step-by-Step Guide
Master the 8-step REW Auto-EQ workflow to generate precise parametric EQ filters for your car audio DSP — from house curve import to filter export.