THD Sweep Measurement

THD SWEEP MEASUREMENT - USER GUIDE

Master the art of measuring Total Harmonic Distortion with style

🎵 THD SWEEP MEASUREMENT

Professional Acoustic Testing Made Simple

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Install

Download THD measurement :

THD sweep measurement April 2026

Install model

Put the model folder : "THD computation" on model database of NVgate. (By default : C:\OROS\NVGate data\Workbook Library\User\ )

Requirement

NVGate V17 or upper.

Option : DC simulated on NVGate front end.

⚡ QUICK START - 30 SECONDS

STEP	ACTION
1️⃣ Launch	Launch NVgate in connected mode and load the THD computation model Double-click THD_Sweep_Measurement.exe
2️⃣ Connect	Put the sweep sine signal on channel 4️⃣ ; put the response on channel 1️⃣
3️⃣ Start	Start the THD_Sweep_Measurement.exe and Click green ▶ START button
4️⃣ Monitor	Watch 4 metrics update live , THD and frequency will also be injected on NVGate channels DC simulated.
5️⃣ Stop	Click red ■ STOP button

✅ That's it! Your first THD measurement is complete. You're now a certified acoustic engineer. (Not really, but it feels good.)

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📊 Four Metric Cards

The heart of the interface. These four numbers tell the whole story:

📈 THD (dB)	📊 THD (%)	📡 Frequency	⚡ Fundamental
Harmonic distortion (log scale)	Harmonic distortion (%)	Current sweep point	Signal strength
+5.42 dB	58.294 %	1234.56 Hz	5.0e-01 V

🎯 UNDERSTANDING YOUR RESULTS

THD (%) - The Easy Number

What is it? Percentage of unwanted harmonics in your signal.

Think of it this way:

• THD 5% = 95% pure signal, 5% noise
• THD 20% = 80% pure signal, 20% noise

The Quality Scale:

🌟 1% - 5%	Excellent - Professional grade equipment
✅ 5% - 15%	Good - Solid speaker performance
⚠️ 15% - 30%	Acceptable - Consumer level equipment
❌ > 30%	Poor - Time for an upgrade 🛠️

THD (dB) - The Technical Number

Same measurement as THD (%) but in decibels (logarithmic scale).

Quick Conversion Chart:

THD %	THD dB	Quality
1%	-40 dB	🌟 Perfect
3%	-30 dB	✅ Great
10%	-20 dB	✅ Good
30%	-10 dB	⚠️ Poor

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⚙️ CONFIGURATION

When Do I Need to Change This?

Honest answer: Almost never.

The default settings work for 95% of users. Only change if your NVGate project has:

• Different window names
• Different marker numbers
• Different DC input addresses

If you're not sure → Don't change anything. It works.

The NVgate Model generate a sweep sine on the output, feel free to modify the settings if you need. We recommand to not put a sweep speed more than 0.05dec/s (or less) in logarithme for accurate results

How to Access Configuration

Click on ▶ Configuration (section expands)

Important Settings

Setting	Default	When to Change
Window (sweep)	Window2	Your sweep FFT has different name
Window (response)	Window1	Your response FFT has different name
Number of harmonics	9

How to Apply Changes

1. Modify field value
2. Click Apply Configuration
3. Log displays "Configuration applied" ✓
4. Done!

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❓ FREQUENTLY ASKED QUESTIONS

Q: I Have only one channels. Can i take the max marker on windows 1 ?

A: Yes, on this configuration, put windows 1 for window (sweep) and select the good number for the marker.

Q: Is THD 5% good?

A: For a speaker? Excellent! You can be proud of that equipment. 🎉

Q: Why does THD change with frequency?

A: Because speakers aren't perfect at all frequencies. Some frequencies cause more distortion than others. That's physics being weird.

Q: Can I use this on any speaker?

A: Yes! Desktop speakers, studio monitors, subwoofers, car speakers - if it's connected to NVGate, we can measure it.

Q: How many times should I measure?

A: Once for curiosity. Three times for reliability. Ten times if you're publishing a paper.

Q: Can I export the results?

A: Yes! Copy text from the log console and paste into Excel, Word, or wherever you need it.

Q: What if my project has different settings?

A: Use the Configuration panel to adjust. It's literally made for this.

Q: Does this work over WiFi?

A: No. It only works locally (same computer or local network). WiFi would add too much latency.

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disclaimer

1) This program is delivered free of charge for NVGate V12. Support is not automatically provided on this tool.

2) For any other requests, please contact your local distributor or the OROS Customer Care department.

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You're Ready!

Go measure some THD and make your speakers proud 🎵

Technical appendix THD Formulas

THD Percentage (DC1)

Formula:

THD(%) = (√(H2² + H3² + ... + H9²) / H1) × 100

Where:

• H1 = Fundamental amplitude (1st harmonic)
• H2, H3, ..., H9 = Harmonic amplitudes (2nd to 9th)
• √ = Square root

Example:

• H1 (fundamental) = 1.0 V
• H2 = 0.02 V
• H3 = 0.01 V
• H4 = 0.01 V
• (all others = 0)

Calculation:

• Harmonics RMS = √(0.02² + 0.01² + 0.01²) = √0.0006 = 0.0245 V
• THD% = (0.0245 / 1.0) × 100 = 2.45%

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THD in Decibels (DC2)

Formula:

THD(dB) = 20 × log₁₀(√(H2² + H3² + ... + H9²) / H1)

Or from THD%:

THD(dB) = 20 × log₁₀(THD% / 100)

Where:

• log₁₀ = Base-10 logarithm
• All H values same as above

Example from above:

• Ratio = 0.0245 / 1.0 = 0.0245
• log₁₀(0.0245) = -1.611
• THD(dB) = 20 × (-1.611) = −32.2 dB

Or: THD(dB) = 20 × log₁₀(2.45 / 100) = 20 × (−1.611) = −32.2 dB

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Quick Conversion Table

THD Percentage	THD in dB	Quality Rating
0.5%	−46 dB	Excellent (pro audio)
1%	−40 dB	Very Good
3%	−30 dB	Good
5%	−26 dB	Acceptable
10%	−20 dB	Fair
30%	−10 dB	Poor
100%	0 dB	Unusable

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Three DC Outputs

Output Channel	Measurement	Formula	Typical Range
DC1	THD %	(Harmonics RMS / H1) × 100	0 to 100%
DC2	THD dB	20 × log₁₀(ratio)	−200 to 0 dB
DC3	Frequency	Sweep frequency at current point	0 to 40 kHz

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Coherence Between DC1 and DC2

The two THD channels always maintain mathematical coherence. Given DC1 value (THD%), you can always calculate DC2:

DC2(dB) = 20 × log₁₀(DC1(%) / 100)

Example:

• If DC1 displays 5.5%
• Then DC2 = 20 × log₁₀(0.055) = 20 × (−1.26) = −25.2 dB

This relationship is guaranteed by the software mathematics.

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Why Two Formats (% and dB)?

THD %:

• Easier to understand for non-technical users
• Direct representation: "5% distortion"
• Useful for product specifications

THD dB:

• Logarithmic scale: easier to see small differences
• Standard in audio/RF engineering
• Used in all standards and specifications
• Better for comparing measurements at different levels

Both represent the same information, just in different scales.

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