A friend handed me a cassette transfer last spring with two problems stacked on top of each other: a steady hiss across all 34 minutes, and a low drone that only became obvious in the gaps between songs. I treated both as one problem, and the result sounded like the tape had been left in a bathtub. To remove hiss and hum in Sound Forge you need two different approaches, because a tonal hum and a broadband hiss respond to completely different tools.
Scope and versions. Tested in Sound Forge Pro 18; tool availability rechecked against the Boris FX Sound Forge product page on July 25, 2026. Boris FX confirms Sound Forge 2026 includes the DeHisser, DeClicker/DeCrackler and DeClipper, but does not yet document restoration menu paths in the detail the MAGIX-era Pro 18 manual did. The paths below are verified against MAGIX-era builds, so check the menus and installed plug-ins in your own edition.
Pick a tool before you start:
- Steady high-frequency hiss, no clean gap to sample → DeHisser
- Stable 50 or 60 Hz hum with visible harmonics → narrow notches, or a dedicated De-hum module
- Hum plus changing broadband noise → noise-print reduction (DeNoiser or an RX workflow)
- Clicks, pops, crackle → DeClicker/DeCrackler
- Noise audible only between phrases → a gentle noise gate, applied last
Part of the Sound Forge Pro 2026 Guide — start there if you’re new to the site.
This guide is part of the Sound Forge Pro Audio Restoration hub.
Identify Tonal Hum, Broadband Hiss, and Low-Frequency Rumble
Hiss is not a separate category from broadband noise. It is broadband noise, usually with more energy in the upper spectrum, which is why we hear it as hiss rather than roar. Tape, preamps, guitar amps and cheap converters all produce it, and depending on the source it can extend across most of the spectrum rather than sitting above a convenient cutoff.
What separates the problems on screen:
- Hum shows as narrow, stable lines at a fundamental and its harmonics. Ground loops, unbalanced cables, dimmers and single-coil pickups cause it.
- Hiss shows as continuous broadband energy with no single line to point at, typically weighted toward the highs.
- Rumble is low-frequency energy from traffic, vibration, wind or footfall. A high-pass filter often handles it faster than any restoration plug-in.
- Fans and HVAC are the awkward case: broadband noise and a few tonal peaks at once, which means one tool rarely finishes the job.
Open Spectrum Analysis before you open a plug-in. On that cassette I pushed a hiss tool harder and harder before I looked at the spectrum and saw the mains line I had been ignoring. The tool was working correctly. I had pointed it at the wrong problem.
The DeHisser: Absorption First, Reduction Second
The DeHisser belongs to the Sequoia-derived restoration toolset included in MAGIX-era Sound Forge Pro builds, and it sits in the Effects menu next to DeClicker/DeCrackler and DeClipper, not under Tools where the older Noise Reduction pack lives. It targets uniform, low-level white noise from microphone preamps and AD converters, and unlike the DeNoiser it needs no noise sample at all. On a continuous performance with no clean gap anywhere, that matters.
The controls are Absorption (1 to 100), Reduction (0 to 30 dB), Music Style, Inverse, Overlap and Resolution. Absorption is the threshold that separates signal from noise, and it is the one that decides whether the result is any good. Set it too low and you get incomplete removal or extra artifacts; too high and you get discoloration, phase-like distortion and chirping modulation. Most people reach straight for Reduction, which is the wrong order.
- Preview at the quietest passage that still has the problem in it, where the noise sits highest relative to the signal.
- Set Reduction to its maximum of 30 dB so you can hear exactly what the algorithm is doing.
- Raise Absorption slowly. It moves through four stages: nothing removed, partial removal with artifacts, complete removal with the signal intact, then removal of the signal itself, which sounds dull and loses the top end. You want the third stage.
- Switch on Inverse to hear what is being subtracted. It should be noise. Breaths, string attacks or cymbal wash mean Absorption is too high. Reduction has no effect while Inverse is on.
- Bring Reduction back down until you have the best compromise between noise removed and sound intact.
- Set Music Style to match the material, which helps the algorithm find transients and de-hiss only between them.
- Raise Overlap for better quality at the cost of CPU. Resolution is signal-dependent, so higher is not automatically better.
Listening to that passage loud with the treble boosted makes the difference between stage three and stage four obvious far faster than listening at a normal level.
On how far to pull Reduction: I stop around 3 to 6 dB on material I care about, but that is a personal habit, not a Sound Forge requirement. The documentation is more specific about the other end. Thirty dB is available, but on extremely quiet passages, where a fading instrument can drop below the noise floor, it recommends limiting yourself to 10 to 15 dB to avoid artifacts.
When the DeHisser Is the Wrong Tool
Once the problem stops being uniform hiss and turns into room tone, HVAC or fan noise, you want a captured noise print instead: Tools → Noise Reduction, select two to five seconds of noise-only audio, Capture Noiseprint, extend the selection to the whole file, preview, apply. Our background noise guide covers the settings and the RX alternative in full.
One point worth correcting, because I have repeated the wrong version myself: noise-print reduction is not blind to tonal problems. The DeNoiser documentation lists mains hum first among the things it was built for, alongside fan noise, sound-card noise, tape noise and feedback, and it has an option that concentrates the correction on tonal components. "Hum first, then broadband" is a useful default, not a rule.
The published material is inconsistent about this. The current Boris FX product page describes the DeHisser as analyzing machine noise and equipment hum, while the DeHisser manual closes by telling you to use the DeNoiser for humming noise. Test both on your own file rather than trusting either description.
Notching Out 50 Hz and 60 Hz Hum
The three built-in equalizers live under Process → EQ. Use the Paragraphic EQ: four overlappable notch bands with adjustable frequency, gain and bandwidth, plus a visual curve. The Parametric EQ handles one filter at a time, so removing several harmonics requires multiple plug-in instances. The four-band Paragraphic EQ is faster for the fundamental and first three harmonics. Our EQ guide compares all three.
The two common mains fundamentals are 50 and 60 Hz, but do not place a notch based on the country alone. Japan runs 50 Hz in the east and 60 Hz in the west, including Nagoya, Kyoto and Osaka, plenty of recordings travel between grids, and tape-speed drift shifts either figure. Find the actual spike in Spectrum Analysis first.
Start narrow. Set a high-Q notch at the fundamental, cut deep, and widen it only until the hum is sufficiently reduced. Then preview against whatever else lives down there: bass, kick resonance, low male voice. A notch that fixes the hum and thins the bass has not fixed anything.
A bass DI I cleaned up in March sat at 49.4 Hz, not 50. Two notches at exactly 50 Hz did almost nothing, and I had already decided the EQ was broken. Engage preview and drag the band's frequency slowly until the drone drops out.
The Harmonics Do Most of the Audible Damage
Killing the fundamental rarely kills the hum. What you hear as buzz rather than drone lives in the harmonics above it: 100, 150, 200 and 250 Hz for a 50 Hz fundamental, 120, 180, 240 and 300 Hz for 60 Hz. Transformer buzz and ground loops push audible harmonics well past 1 kHz.
Four Paragraphic bands cover the fundamental plus three harmonics. If you need more, chain a second Paragraphic EQ instance in the Plug-In Chainer, or use a dedicated De-hum module, rather than committing several destructive passes. RX De-hum is an option if your install has iZotope RX Elements. Some MAGIX-era Suite editions bundled it; Boris FX has not clearly documented RX inclusion for every Sound Forge 2026 edition. The harmonic limit depends on the RX generation: older De-hum documentation describes up to seven harmonics, RX 9 expanded Static mode to 16, and current RX 12 Elements supports 16 static harmonic bands.
Stacking notches has a cost. iZotope's engineers wrote a detailed piece on filter ringing that makes the point cleanly: notching only the fundamental and first harmonic, when both sit below the useful signal range, can be close to transparent. Ringing becomes likely once further notches cut through frequencies the voice or instrument actually occupies, because transients set the filters ringing audibly.
On speech I stop after the strongest harmonics and test a gentle high-pass below the useful vocal range. Where that cutoff lands depends on the speaker, so preview it rather than defaulting every voice to one number.
Audition What You Are Removing, Not Just the Result
Use Preview with whichever comparison control the plug-in gives you: Bypass, Inverse, Output Hum Only, or a host-level bypass. Bypass tells you whether the file sounds better. Inverse and Output Hum Only tell you why, by letting you hear what is being subtracted. If your voice is audible in the removed signal, no amount of A/B on the output makes that acceptable.
Loop the quietest passage in the file, not the loudest. Loud material masks artifacts, quiet material exposes them. Check on more than one system too. Notches at 50 or 60 Hz and their first harmonics sit in a range many laptop speakers reproduce weakly or inaccurately, so a low-end problem can stay hidden until you listen on full-range monitors or headphones.
Artifacts and Knowing When to Stop
The metallic chirping that ruins over-processed audio is a known property of spectral subtraction, not a bug. The DeNoiser documentation puts the residual artifact level around 20 dB below the original noise, and notes the ear still reacts to it sharply because it sounds synthetic.
Work through it in order. Improve the noise profile or Absorption setting first, then reduce the processing amount. An inaccurate profile and an overly aggressive reduction can both produce chirping, smearing or dullness. Then use the artifact suppression controls where the plug-in offers them, and accept a higher residual noise floor, because leaving some original noise in place is a legitimate result.
A second light pass sometimes helps, but it can also compound smearing and dullness, so compare it against one conservative pass first. If the noise survives everything, check that it is the problem you think it is: intermittent buzz and impulse noise need click and crackle removal, and noise that only bothers you between phrases is a job for a gentle noise gate.
Frequently Asked Questions
Where is the DeHisser in Sound Forge?
Under the Effects menu, alongside DeClicker/DeCrackler and DeClipper, and also reachable through FX Favorites and the Plug-In Chainer. The older Noise Reduction pack sits under Tools.
Should I remove hiss or hum first?
Hum first is a good default, because narrow notches leave the rest of the signal alone. It is not an absolute rule: the DeNoiser is documented for mains hum too, and with a clean sample it can handle both.
Is my hum 50 Hz or 60 Hz?
It depends on the grid where the audio was recorded, not where you are editing. Rather than guessing from the country, open Spectrum Analysis and find the lowest stable spike. Japan alone splits 50 Hz east and 60 Hz west, and tape-speed drift can put the real fundamental a couple of Hz off either figure.
How much hiss reduction is too much?
Set Absorption first, switch on Inverse to confirm only noise is leaving, then raise Reduction as far as the source tolerates. The DeHisser goes to 30 dB, but on extremely quiet passages the documentation recommends staying between 10 and 15 dB to avoid artifacts.
Why does my audio sound metallic after noise reduction?
Spectral subtraction leaves a synthetic residue when it removes too much. Improve the noise profile or Absorption setting first, then lower the amount, then use the artifact suppression controls. A second lighter pass can help, but it can also worsen smearing, so compare before committing.
Will removing hum affect my bass?
It can. A narrow notch limits the damage, but the fundamental and its harmonics can overlap with bass notes, kick resonance and vocal fundamentals. The wider and deeper the notch, the greater the tonal loss. Preview against the low end rather than trusting the frequency number.
Sources checked July 25, 2026: the Boris FX Sound Forge product page, the Boris FX-hosted DeHisser and DeNoiser documentation, JNTO, and iZotope RX De-hum material. Our 2026 review covers where the toolset stands under the new owner.