It’s nice to have the tools and skills to clean up noisy audio files. Perhaps when you’re digitizing old and prized family tape recordings, or when you’ve captured a great interview for a podcast and there’s an annoying background noise.
Nothing can be perfect, but there are many ways to improve your audio files. Amazingly, many of these tools are built into the free and open source audio editor Audacity.
Audacity can be used as an audio recorder with multiple microphones, or it can work with existing audio files (WAV, MP3, OGG, AIFF, etc.). In this how-to we will tackle pre-recorded audio that needs cleaning up.
Install Audacity
1. download Install Audacity on your operating system.
2. [ファイル]>>[インポート]Click to rip the target audio file.Audacity handles many audio file types, common uncompressed WAV and AIFF files, equally common compressed MP3 files, but also less common types such as OGG and FLAC files without problems.
3. Click the play button to listen to the file. A waveform represents an audio file. One waveform shows a mono recording, two waveforms represent a stereo audio file (left and right channels).
Problem identification
When trying to clean up audio, the first thing you should consider is what is causing the poor audio. Common failures may include high-pitched hissing sounds in the background, audio being too loud and “clipping” on parts of the track, resulting in large crackling.
Other issues could be background noise in the recording, such as wind noise hitting the microphone, a train rumbling in the distance, or the audio simply being too quiet. It’s worth listening to the target audio file a few times and noting the problem areas and times you want to try and improve.
1. follow the record When Press the spacebar to stop and start audio playback. This resets playback to the cursor position, which is useful if you want to hear the same short section repeatedly.
2. Pause playback by clicking the “p” button on your keyboardThis pauses the playback position and allows you to note the time position, which is useful for making a list of problem locations in the file.
audio distortion cleanup
Now you have a list of potential problems. Let’s take a look at some approaches to improve audio.
Our test audio had a small explosive click in the audio, the VU meter flashed into the red section, and the headphones briefly distorted. can magnify the problem.
You can’t reduce audio distortion at this point, but you can simply reduce the amplitude of this portion of the waveform. This means that even if it distorts momentarily, the speaker will not pop and annoy the listener.
1. Click slightly to the left of the problem area When drag the region to the right You can highlight this small section of clipped audio.
2. [効果]Click the dropdown menu. When Select “Amplify”.
3. decrease the amplification value Enter a negative value in the “Amplification (dB):” input box or use the slider. Try lowering the value to -1dB and click the OK button. The height of the highlighted area of the waveform decreases.
Four. listen to the new version Check if the issue is resolved. Look at the VU meters and see if the problem causes the output to clip and show a red line on the meters. Of course, you can use control and z to undo the adjustment, or go back to the amplification effect for further reduction or adjustment.
hiss removal
For the next audio problem, let’s take a look at the classic high-pitched hiss in the background of an audio recording. This could be due to wind noise or an overly noisy AC unit. There are several different approaches we can try to achieve this. The first approach to consider is using a lowpass or notch filter to essentially cut the hiss frequency region from the audio file. But before we do that, we need to identify where the problem lies.
1. select all audio,[分析]from the drop down menu[スペクトルのプロット]Click. The Frequency Analysis window lets you see all the frequencies contained in your audio file. It doesn’t have to be fully understood to be useful, but the basic premise is that high frequencies are on the right side of the diagram and low frequencies are on the left.
Most music has some audio information in all frequency ranges, but a simple recording of voice, for example, may only use a certain portion of the range. This means that it is possible to cut entire frequency ranges without affecting the target audio in the file. For high-pitched hiss issues, you may also see stand-alone spikes in the high frequencies where the hiss is being pitched. By reading the X-axis of the plotted spectrum, we can note the frequency regions where hiss is present. This is useful for targeting the filter to remove hiss.
2. Note the frequency affected by hiss (x-axis).
3. To remove high-pitched hiss, Select waveforms for all audio files and from the effect dropdown Select a low pass filter.
Four. Enter a value slightly below the hiss frequency in the frequency entry field. after that Set roll-off value Via input box. MeIf your hiss was at 1500 Hz, you can set the filter frequency to 1400 Hz and tweak the rolloff value as needed.
Five. Hear the preview. You should notice a reduction in hissing noise. If you are satisfied with the result, [OK]Click to apply. If not, go back to step 4 and fine tune the frequency/rolloff.
A notch filter is a filter that reduces all frequencies in the frequency response in a notch fashion. This is useful if you have a recording where there is probably some hiss but using a lowpass filter could affect other parts of the audio. For example, if you have a recording of a percussionist playing a lot of cymbals, removing high-pitched hiss might affect the sound of the cymbals as well.
1. From the effect, Select a notch filter.
2. Fine tune the target frequency (which will be the center of the notch) and Click Preview.
3. Increase or decrease the Q value of Wider/narrower notch. click preview The results can always be reversed, so it’s worth hearing as you iterate through the filters and replot the frequency spectrum to fine-tune your approach.
Finally in the filter you can use a frequency selective high pass filter. Everything below that frequency is reduced, but above it is unaffected. A high-pass filter is often a good solution for recording distant train roars and other low-frequency artifacts.
1. Click Effects >> High Pass Filter.
2. To eliminate the low-pitched rumble, Select audio file waveform and from the effect dropdown Select a high pass filter.
3. In the frequency input field, Enter a value slightly higher than the rumble frequency and set the rolloff value from the input box.MeIf the rumble was 1000Hz, you can set the filter frequency to 1100Hz and tweak the rolloff value as needed.
Four. Hear the preview. You should notice a reduction in hissing noise. Once satisfied with the results,[OK]Click to apply. If not, go back to step 3 and fine tune the frequency/rolloff.
Add Noise Reduction
Sometimes you have a recording with a more complex collection of unwanted noise. In these difficult situations it is useful to try the “noise reduction” effect. This effect is especially useful when the recording contains only unwanted noise and has sections with no target audio. In fact, if you’re recording on site and you know your recording will have unwanted noise, it can be very helpful in properly recording the unwanted stuff.
1. Highlight sections of an audio file that contain only unwanted noise. A 44.1 kHz WAV file should be at least 0.05 seconds long, but it’s not uncommon to choose more than a few seconds.
2. Click Effects >> Noise Reduction.
3. [ノイズ プロファイルを取得]Click the button.The window closes quickly, but in essence it’s setting the effect with a sample of what you want to remove.
Four. Select file area I want to apply the noise reduction effect
5. Again Activate the noise reduction effect When Fine-tune the values in the Step 2 section. in the lower left corner of the dialog box[プレビュー]Click the button to hear the effect of your settings.
6. [OK]Click. Apply noise reduction.
These approaches give you a great basic toolset for solving a wide variety of audio file problems. Once satisfied with the results, File – Export Creates a new, cleaned audio file.
