Intermodulation Frequency Calculator

Calculate two-tone and three-tone intermodulation products, locate in-band spurs, fold products through a digital sample rate, and compare spacing against audio, wireless, and RF guard bands.

🎛 Intermodulation Presets

Choose a real measurement or frequency-planning scenario, then adjust the tones, product order, bandwidth, and sample-rate folding. Frequencies may be entered in Hz, kHz, or MHz.

📈 Frequency Plan Inputs

Frequency unit All three tones use this display unit.

Primary tone f1 First carrier, test tone, oscillator, or blocker.

Secondary tone f2 Second tone used for IM2, IM3, IM5, and higher products.

Optional third tone f3 Set above zero to include 3-tone products.

Maximum product order Order is the sum of absolute tone coefficients.

Product family 3-tone mode adds combinations such as f1 + f2 - f3.

Protected band low Products inside this range are counted as in-band.

Protected band high Use audio bandwidth, receiver passband, or assigned block.

Guard distance from wanted tones Flags products landing close to f1, f2, or f3.

Duplicate merge tolerance Products closer than this are grouped as the same spur.

Sample rate for alias check Set 0 to skip folding; otherwise Nyquist equals Fs / 2.

Products shown in detail The count summary still uses the full generated set.

Enter positive f1 and f2 values, keep the protected band high above the low edge, and use non-negative guard, merge, and sample-rate values.

Closest In-Band Spur

0 Hz

nearest protected-band product

In-Band Products

unique products after merge tolerance

Worst Order

3rd

lowest-order in-band risk

Alias Risk

folded products inside band

Run a calculation to see whether the frequency plan is guard-band limited, alias-limited, or mostly clean.

Calculation Breakdown

📐 Four Core Formulas

2-Tone Product

fIM = |m f1 +/- n f2|, with order = m + n

3-Tone Product

fIM = |a f1 + b f2 + c f3|, order = |a| + |b| + |c|

Alias Fold

fAlias = |((f + Fs / 2) mod Fs) - Fs / 2|

Guard Margin

margin = minimum distance from product to each wanted tone

🔎 Current Frequency Plan Spec Grid

1 kHz

Tone spacing f2 minus f1

24 kHz

Nyquist limit from sample rate input

Raw products before merge and filtering

0.5 kHz

Guard distance around wanted tones

📋 Closest Intermodulation Products

Formula	Order	Product	Alias	Nearest wanted	Status
Run the calculator to list the closest products.

📚 Product Order Reference

Order	Common form	Why it matters	Typical severity
2nd	f1 + f2, \|f2 - f1\|	Can create sum, difference, and low-frequency beat products.	Usually easier to filter unless it lands inside the passband.
3rd	2f1 - f2, 2f2 - f1	Often lands close to the original tones and is hard to filter.	High priority in RF coordination and audio linearity tests.
5th	3f1 - 2f2, 3f2 - 2f1	Appears near wanted channels when devices are driven harder.	Important for dense wireless and wideband front ends.
7th	4f1 - 3f2, 4f2 - 3f1	Lower amplitude than 3rd order but still relevant in crowded plans.	Medium risk unless spacing is very tight or levels are high.
9th	5f1 - 4f2, 5f2 - 4f1	Useful for conservative checks on many-carrier systems.	Usually low amplitude, but worth reviewing near receivers.

🎚 Audio And RF Band Reference

System	Useful band	Product concern	Planning note
Audio converter test	20 Hz to 20 kHz	Difference tones and folded ultrasonic products.	Check the alias column when tones exceed Nyquist.
FM broadcast receiver	88 to 108 MHz	Strong adjacent transmitters can create in-band IM3.	Use protected band low/high around the receiver range.
Wireless microphone block	470 to 608 MHz	Third and fifth order products between assigned carriers.	Guard products away from active channel center frequencies.
IEM transmitter rack	470 to 698 MHz	Combining several transmitters raises composite IMD risk.	Use conservative order settings for dense show files.
HF or VHF receiver	System dependent	Out-of-band blockers can mix into the tuned channel.	Include blocker frequencies even when they are outside the passband.

🎵 Common Scenario Starting Points

Preset	Tones	Band	Primary result to watch
Audio 19 kHz + 20 kHz	19 and 20 kHz	0 to 24 kHz	1 kHz difference tone and ultrasonic alias products.
Guitar Pedal 700 + 1900	700 Hz and 1.9 kHz	20 Hz to 20 kHz	In-band musical IM3 products around 500 Hz and 3.1 kHz.
UHF Wireless Trio	521.2, 523.8, 526.4 MHz	520 to 528 MHz	3-tone products near assigned carriers.
FM Broadcast Check	94.7 and 99.5 MHz	88 to 108 MHz	2f1 - f2 and 2f2 - f1 landing inside the FM band.
ADC Alias Stress	21 and 23 kHz	0 to 24 kHz	Products above Nyquist folding back into audio.
Synth Oscillator Pair	440 and 660 Hz	20 Hz to 20 kHz	Harmonic-related products that can mask intentional partials.

📏 Guard Band Comparison

Use case	Small guard	Moderate guard	Conservative guard
Audio distortion testing	10 Hz around tone	50 Hz around tone	100 Hz around tone
Synth or instrument analysis	5 Hz around partial	20 Hz around partial	50 Hz around partial
Wireless microphone carrier	25 kHz from center	100 kHz from center	250 kHz from center
FM broadcast receiver	100 kHz channel edge	200 kHz channel spacing	400 kHz local-clear margin
Wideband RF front end	1 percent of span	2 percent of span	5 percent of span

💡 Intermodulation Tips

Start with third order. The products 2f1 - f2 and 2f2 - f1 often sit close to wanted tones, which makes them much harder to remove with ordinary filtering.

Fold digital products. In converter testing, a product above Nyquist can still become audible after sampling. Use the sample-rate field to check its folded frequency.

Use real guard units. A 0.5 kHz guard is huge for audio but tiny for UHF wireless. Match the unit and guard setting to the system being coordinated.

Check three carriers together. Wireless and RF systems can pass a two-tone check while still failing from f1 + f2 - f3 products in a dense group.

Why is it that you have several wireless mics on stage and live sound system sounds weird? You may not care about intermodulation from an RF engineering standpoint, but they’re no theoretical phenomenon. Mixers and amplifiers will produces frequency components that didn’t originate in the source signal. In other words, phantom tones can mess up your critical communications channels or any audio. The calculator above does the math for you, but knowing what causes them to occur help you solve the issue before it blows up your show.

Begin by adding your primary and secondary tones. A common misconception here is that widely spaced frequencies won’t interfere with each other. Unfortunatly, third order results (for example: two times one tone minus another) will tend to end up near original tones no matter how far apart they are. Because these occur in the passband where you desire clean signal, they’re hard to eliminate with filters like high- or low-pass. The solution doesn’t live next to your voice; it’s not something you can easily filter away.

How to Fix Weird Sound Problems

For complicated wireless mics and IEM rigs, two tones isn’t sufficient to account for all the interactions. A third tone adds products like one plus two minus three. They might be below second-order distortion products but show up at precisely the frequencies that is problematic. The tool has options to turn on this mode and set maximum product order to consider. If you have lots of channels in a given frequency block or if your system is pushed hard, higher orders will makes a difference.

Planning is where it all starts with guard bands. Even when two products don’t quite overlap, setting a conservative margin around desired tones will flag items that fall within the margin. Because human hearing tends to merge adjacent frequencies, a modest guard band is sensible for audio use. But larger margins are necessary for RF applications, to avoid desensitizing receivers. The table below (on page) show suggested spacings for common uses. Use this as a starting point for what’s reasonable to expect from your own gear.

Aliasing adds another wrinkle to digital conversion. Intermodulation products at or above one-half the sample rate fold back in on themselves. This becomes either ultrasonic noise (noise above human hearing) or distortion in the midrange. That’s all invisible until post-analog-to-digital conversion. The alias column points out hidden risks that even traditional frequency planning totally overlooks. It is a minor point but a significant one when fidelity is most important, whether you’re broadcasting or simply recording audio.

What it shows are the worst offending order and the corresponding close-in spurs. So then you know if it’s simple harmonics mixing (basic problem) or something more complicated like nonlinear effects. Are there a lot of third-order products? It is time for some more linear components in that front end. Are there lots of high orders? Maybe time to add some more filters or reduce drive level. In real life you should of balance those requirements with what equipment you have, what bandwidth you want to use etc.

Intermodulation management is an exercise in anticipating chaos. By plotting out where those ghostly frequencies show up, you can take command of a system that would seem to have no predictability at all. It’s simple math but with serious consequences for signal integrity. Knowing what you cannot see. The invisible interference that comes through your receiver input or your ear, makes all the difference between clean audio and garbled conversation.