Use a time-frequency edit when one known moment and frequency range need changing. Choose dynamic EQ when the correction should follow changing levels. This Mac workflow uses synthetic tones to make that decision concrete.

The task here is to reduce a high tone during one short section of a generated, two-tone sound while retaining its lower tone. You will generate the example in Audacity and edit the exported audio in REAPER. The settings are illustrative starting points, not results from a listening test.

What determines whether you need a time-frequency edit?

Write down the condition that should cause the correction. “Reduce this frequency between two and three seconds” describes an edit tied to time. “Reduce this frequency whenever it becomes too loud” describes level-dependent processing. Audacity documents spectral selection as a combination of time and frequency boundaries; REAPER’s effects guide documents frequency-dependent thresholds in its spectral compressor. These provide the two different forms of control used in this comparison. Audacity: Spectral Selection and Editing, REAPER Effects Guide

For this example, imagine that a 2,000 Hz component is wanted throughout a six-second sound, except during seconds two to three. Its level does not change before that interval. A level detector has no reliable signal-level distinction telling it that the middle second deserves different treatment. A time-frequency region expresses that instruction directly.

That conclusion is an inference from the processing rules, not an assertion about which tool sounds better. You could also automate an EQ band over the chosen interval. That remains a sensible option when you already have an EQ configured; the practical advantage of a spectral region is that you can place the time and frequency boundaries together.

Use this decision aid before adjusting any controls:

Your intended change Useful starting approach Reason
Reduce one frequency component during one known interval Time-frequency edit You can identify exactly where the change belongs.
Reduce a recurring frequency component only when its level rises Dynamic EQ or frequency-dependent compression The correction needs a level rule.
Reduce the same frequency throughout the sound Static EQ No changing time or level condition is needed.
Lower every component during one interval Volume envelope Frequency selection adds unnecessary work.
Change a component that still exists on its own source track Edit that source first You can avoid processing the combined sound.

The final row matters for generated audio. Keep the original components when you can. The following exported example deliberately combines them so you can practise choosing a frequency-specific edit on an existing audio file.

How do you create a useful synthetic example?

Use two steady sine waves rather than a complex preset. Audacity’s current documentation exposes waveform, frequency, amplitude and duration through Generate → Tone. A sine wave supplies one frequency component, making the intended selection straightforward. Audacity: Tone

In a new Audacity project, create the following two mono tracks. The current menu command is Tracks → New mono track. Select only the track you intend to generate into and place its cursor at time zero before opening the generator. Audacity: Tracks

Track Waveform Frequency Amplitude Duration
Lower component Sine 500 Hz 0.10 6 seconds
Upper component Sine 2,000 Hz 0.05 6 seconds

Generate the lower component first. Add the second track, select it alone, return the cursor to zero and generate the upper component. Confirm that both begin together and last six seconds. Audacity starts generation at the selection’s beginning, or at the cursor when no range is selected. Audacity: Tone

Keep both tracks unmuted, with their track gains unchanged. Choose File → Export audio, set Type to Export full project audio, and export a WAV file named two-tone-original.wav. This export mixes the project into one file; saving the project separately retains the component tracks for later changes. Audacity: Export your audio, Audacity: Export Menu

The target is deliberately specific: reduce the 2,000 Hz component during seconds two to three while retaining the 500 Hz component. The high tone outside that interval should remain wanted. This is an editorial instruction you impose on the example, not a defect discovered by measurement.

How do you apply the time-frequency edit in REAPER?

The following path follows section 7.39 of the REAPER 7.84 user guide, available through the official documentation page. Import two-tone-original.wav into a new REAPER project and position it at zero. REAPER User Guide

  1. Right-click the audio item and choose Spectral edits → Show spectrogram.
  2. Make a time selection from two to three seconds.
  3. Right-click the item and choose Spectral edits → Add spectral edits to item.
  4. Drag the region’s upper and lower edges around the 2,000 Hz component, excluding 500 Hz.
  5. Reveal the region controls by clicking its edge or centre bar. Lower Spectral region gain; try approximately −6 dB as an illustrative starting point.
  6. Add time and frequency fades, then compare using Bypass spectral edit. Up and Running: A REAPER User Guide, section 7.39

Start with a frequency range comfortably separating the two tones—for example, roughly 1,800–2,200 Hz. That range is a selection aid for this example, not a universal bandwidth recommendation. Keep the level reduction moderate while establishing the boundaries. A large reduction can make a misplaced region harder to evaluate constructively.

The useful comparison has three parts: the sound before the edit, the edited interval, and the return to the original sound afterward. Listen across each boundary, then compare the complete six seconds. Decide whether the timing communicates the intended change rather than merely making the selected region quieter.

REAPER’s item spectrogram is before track effects, so it does not display changes caused by those effects. Stereo spectral edits also affect all channels by default. Start with this mono example to avoid adding channel decisions. Up and Running: A REAPER User Guide, section 7.39

When would dynamic processing be the better choice?

Change the instruction: suppose the upper component now varies in level, and you want to restrain only its louder passages wherever they occur. Drawing a separate region for every occurrence would encode each event manually. Level-dependent frequency processing can instead express one reusable rule.

Keep the application terminology precise. REAPER documents ReaEQ as a parametric equalizer. Its documented stock alternative for frequency-dependent compression is ReaFir in Compressor mode, rather than a conventional dynamic bell-EQ interface. REAPER Effects Guide

For that alternative, open the track’s FX window, add ReaFir, and choose Compressor under Mode. Its red curve represents frequency-dependent thresholds. Keep thresholds high outside the target area; lower the curve around the upper component and try a modest Comp Ratio, such as 2:1. Adjust against the actual input display rather than copying a threshold from another file. These values are starting suggestions. REAPER Effects Guide

The documented limitation is consequential: FFT Size affects both frequency-band resolution and effective attack/release times. Larger sizes produce longer effective response times. Lowering thresholds excessively can introduce distortion. Those controls make ReaFir a supported way to explore frequency-dependent dynamics, but they do not make it interchangeable with every dynamic EQ. REAPER Effects Guide

On the original steady-tone example, threshold processing cannot identify the requested middle second from level alone once its response has settled. Adding automation could supply that timing, but then you are explicitly adding the time rule that a spectral region already describes.

What should you check before keeping the edit?

Use these checks to finish the task rather than repeatedly deepening the cut:

  • Timing: Does the reduction start and end where you intended? Include surrounding audio in the comparison.
  • Frequency scope: Is the region centred on the upper component and clear of the lower one?
  • Transitions: Do the edit boundaries need gentler fades?
  • Wanted content: Would a narrower region or smaller reduction preserve more of the intended sound?
  • Source access: If the separate generated components remain available, would editing the upper source track be simpler?

A frequency selection cannot distinguish wanted and unwanted material occupying the same selected band and moment. Audacity explicitly notes that removing a band also removes wanted sound within it. Treat that as a limit on the achievable outcome, especially when moving beyond this deliberately separated two-tone example. Audacity: Delete selection

For a fixed generated file, choose the smallest intervention that expresses your intention clearly. Use a time-frequency edit for a known local change, dynamic processing for a recurring level condition, and the original generator or component track when it offers a more direct adjustment. Keep the original file so that the final choice remains easy to revisit.

Sources