How to Record Audio Samples at Home, Using an iPhone
Did you know you can record in stereo on an iPhone? I didn’t — that is, until a few weeks ago, when I searched on YouTube for “record in stereo on an iPhone” and found literally one video demonstrating it (and then another by the same guy). So I tried it that night, which happened to be the Fourth of July, and recorded my neighbors lighting fireworks. And I was impressed; the audio was clean and clear, with high dynamic range, transparent compression, and virtually no distortion. So I’ve spent the past few weeks researching iPhone signal processing, recording audio, and developing a workflow for producing audio samples using an iPhone and Logic Pro, and what follows is all I’ve learned. I hope you find this information useful.
Below are stereo recordings I made on my iPhone 11 Pro Max. The first is that of my neighbors lighting fireworks, and the second is a consolidation of various items around my house. I have gain-matched and normalized the recordings, but they are otherwise raw.
Preparing to Record
⏩ Find a room in your home with the least amount of reflections (or, at least, the most pleasant reflections), apply acoustic treatment to hard surfaces, and turn off noisy devices and appliances.
Step 1: Pick a Room
Pick a room in which to record. Find the room in your house with the least amount of reflections (or, at least, the room with the most pleasant reflections). You can determine this by standing in the middle of each room and making a short loud noise, such as clapping your hands. Smaller rooms may sound boxy (or cramped and boomy, as if you were inside a box), and larger rooms may sound cold and empty; unless your intention is to capture sounds as they interact with such rooms, a happy medium — say, a bedroom — is best.
Step 2: Apply Acoustic Treatment
To capture pure sounds and clean signals, eliminate (or at least minimize) the potential for sonic disturbances and distortions by acoustically treating your recording room. Although acoustic treatment itself may be complex, the physics of it is simple: Sound waves bounce, or reflect, off hard surfaces, and are absorbed by soft surfaces. So grab blankets, pillows, and cushions, and cover as many surfaces as is necessary to produce a pleasant, even sound.
💡 To cover the ceiling, either build a fort, or, if your recording room has a ceiling fan, slip pillows between the ceiling and the blades of the ceiling fan.
As you treat your recording room, locate points of reflection by periodically doing as you did when searching for the room, and clap your hands. The reflections should concentrate in specific areas of the room, which areas will become increasingly obvious as you place your makeshift dampeners and diffusers. Note, however, that the areas in which the reflections concentrate are not necessarily where you want to place treatment, as the reflections are likely beginning elsewhere and ending in the areas of concentration. So try different configurations until you discover what works best for your room.
Step 3: Remove Unwanted Noise
iPhone microphones are sensitive and capture a wide dynamic range of sound, so remove as much interference as possible. This includes turning off cieling fans, light bulbs, and especially air conditioners (and, if you live in a small space, and if it’s safe to do so, refrigerators too). Also, depending on the sounds you plan to record, consider wrapping your iPhone in a sock or two to protect the microphones from whooshes and plosives; this step isn’t necessary, but you may find it useful for some sounds, especially when close-miking.
⏩ To ensure that your recordings are effective and that your recording sessions are efficient, have a plan, set limitations, decide beforehand whether to record in mono or stereo, position your phone optimally, and record to a click track.
The following are tips for recording audio using an iPhone. Some are more suited to structured recording sessions, but all are useful to consider. If you prefer a less structured process, though, then by all means, ignore these tips and dive straight into recording.
Tip 1: Have a Plan
Know what you would like to record — meaning, know what sounds you wish to capture and for what purpose(s) you wish to capture them. If it helps, create a list.
Tip 2: Set Limitations
To make your recording session easier to manage, and to make editing and selecting samples later easier to accomplish, limit the number of sounds you plan to record as well as the number of takes per sound, the amount of time spent recording each sound, or the length of your recording session.
Tip 3: Decide Whether to Record in Mono or Stereo
This decision will depend on the sounds that you plan to record as well as your intentions for the resulting samples. Generally, stereo recording is good for capturing ambience or spacial information relative to sounds, and mono recording is good for capturing everything else. To record in mono on an iPhone, simply use Voice Memos; to record in stereo, simply record a video.
💬 If you plan to record in stereo by recording a video, first check your Camera settings, as “Record Stereo Sound” may be toggled off, in which case you’ll need to toggle it on.
Technical note: There are four microphones on an iPhone: upper back, upper front, first bottom, and second bottom. For stereo recording, Apple captures independent but simultaneous input from all these microphones and then combines them into a stereo signal by determining both the orientation of the iPhone (portrait, portrait upside down, landscape left, or landscape right) and the location of the sound source when recording, and then processing the signals from each microphone accordingly. And all this happens in real time, based on the time delays between signals. This means that each microphone plays a unique role in capturing stereo audio, and both the quality and qualities of the audio are dependent on which microphone is favored. So, to determine where or how to place your iPhone relative to the sounds you wish to record in stereo, first decide the orientation of your iPhone, as this will indicate the directions of the microphones (and thus which microphone to favor).
Technical note (continued): When using the back-facing camera in portrait orientation, the iPhone designates the direction of the back-facing microphone (upper back) as forward, the front-facing microphone (upper front) as backward, the left bottom-facing microphone (first bottom) as left, and the right bottom-facing microphone (second bottom) as right. When using the front-facing camera in portrait orientation, these directions are all inverted, as Apple orients the directions of the microphones from the perspective of the observer, not the subject. Your intuition about microphone directions in landscape orientations will probably be correct, but if you’d like to learn more about iPhone orientations, beamforming, and microphone directions, see the source of this information, this presentation from WWDC20:
Record stereo audio with AVAudioSession - WWDC 2020 - Videos - Apple Developer
Stereo recording is a powerful way to deliver immersive sound to listeners, fans, and family - and your app can use the…
💡 For the iPhone to effectively process a stereo signal, and for best results generally, the iPhone needs input from every microphone. So avoid obstructing any of the microphones with the iPhone’s placement; for example, suspend the iPhone — either by holding it or by mounting it to something open and sturdy, like a tripod — instead of laying it on a surface.
💡 When recording in mono, the perceived location of a sound source from the perspective of the listener will always be the same (straight in front, or right down the middle), so subtle movements of your iPhone will have a negligible effect on both the sound quality and the listener’s experience. However, when recording in stereo, the perceived location of a sound source from the perspective of the listener will move relative the movements of your iPhone, so even subtle movements can have a major effect on the sound quality as well as the listener’s experience. So either remain still while recording, or mount your iPhone to something sturdy.
Tip 4: Watch Your Proximity
The quality of a sound is determined by many factors, a crucial one of which is the proximity of the microphone to the sound source. Shorter distances will yield more intimate recordings, as they capture more of the sound itself and less of the reflections of the room, but they also capture frequencies unattenuated by air, thus tending to distort or otherwise sound unnatural, and often producing a lot of mud. In contrast, larger distances will yield more distant recordings, as they capture less of the sound itself and more of the reflections of the room, which can be good or bad depending on your intentions. As with most things, a happy medium (about a foot or two away from your iPhone) is best.
Tip 5: Record to a Click Track
Recording to a click track is useful in general, as doing so organizes both your recordings and your recording session, but it is especially useful if your intention is to sample instruments, as doing so will expedite the post-production process as well as enable general coherence across your samples. This article, however, deals less with sampling instruments than it does with recording loose samples, so for information about (and inspiration for) sampling instruments, I recommend Spitfire Audio cofounder Christian Henson’s excellent YouTube channel:
Christian Henson Music
Adventures in the composing and sampling trade with an insight into life as a W.I.L.L.I.E.
Extracting Audio from Videos
⏩ To extract stereo audio from video recordings, create a Siri shortcut that prompts you to select a video, encode the video as audio, save the audio to iCloud Drive, and then delete the video from your camera roll.
If you’ve chosen to record in stereo by recording videos, you’ll need to extract the audio from the videos to create your samples. You can do this by importing the videos into Logic Pro, or by opening the videos in QuickTime Player and then exporting the videos’ audio. However, the most efficient method is to create a Siri Shortcut that will prompt you to select videos from your camera roll to be encoded as audio, save the resultant audio files to your iCloud Drive, and then delete the videos from your camera roll. The benefit of this method is, of course, its efficiency, as it takes you step by step through the process, and all with a single tap.
The steps for creating this shortcut are as follows:
Step 1: Create a Shortcut
- Open Shortcuts and tap the blue plus icon.
Step 2: Add an Action to Select Input
- Tap Add Action.
- In the actions search bar, enter “Select Photos”, then tap this action to add it to your shortcut.
- Within the Select Photos action, tap the blue disclosure button to display options for configuring the action.
- Under Include, tap All, deselect Images and Live Photos, and then tap Done.
- Toggle on Select Multiple.
Step 3: Add an Action to Encode the Selected Input as Audio
- In the actions search bar, enter “Encode Media”, then tap this action to add it to your shortcut.
- Within the Encode Media action, tap the blue disclosure button, then toggle on Audio Only, and set the format to AIFF.
Step 4: Add an Action to Save the Encoded Input as an Audio File
- In the actions search bar, enter “Save File”, then tap this action to add it to your shortcut.
Step 5: Add an Action to Delete the Selected Input
- In the actions search bar, enter “Delete Photos”, then tap this action to add it to your shortcut.
- By default, the action will link to the previous action, thus passing into it the saved files. However, the files you want to delete are, not the saved files, but the original files. So, to select the original files, tap the variable (the blue “Saved File”) and then, in the menu that appears, tap Clear Variable.
- In the Delete Photos action, tap the variable again (now a faded blue “Photos”), and, in the menu that appears, tap Select Magic Variable and then select the Photos magic variable.
Step 6: Configure the Details of the Shortcut
- Rename the shortcut (for example, “Extract Audio from Video”), and change its color and glyph.
- Tap the close button to save the shortcut.
💬 At WWDC20, Apple released an API feature for stereo recording, so I hope to see more developers implementing it, including Apple. In the meantime, this workaround is reasonable.
In the following paragraphs, I will describe a Logic Pro workflow, as this is the program I use. However, the steps will be identical in other programs; the tools may simply be called by other names. Also, the order of these steps is relative to me, of course, so alter it if doing so works better for you.
Step 1: Import
Import your recordings either by choosing File > Import > Audio File… or by dragging and dropping the files into the Logic Pro Workspace.
Step 2: Remove Silence
To quickly isolate and distinguish the important elements of your recordings, remove all silent passages from the audio regions. The steps for doing so are as follows:
- Above the track header area, choose Functions > Remove Silence from Audio Region…
- In the Remove Silence window, configure the parameters. Of most importance is the threshold value, which determines the level below which the signal will be considered silence and as such removed. Enabling Search Zero Crossing will prevent pops and clicks.
- Press OK.
Step 3: Cull
Play through the new regions and remove all that are unfit for your purposes. To make culling easier and more efficient, and to ensure that you retain only the best samples, set criteria by asking yourself the following questions (or similar questions):
- What is your aim with these samples?
- Who are these samples for?
- How do you intend for these samples to be used?
Also consider setting rules, such as these:
- If you don’t like a sound, delete it.
- If you’re unsure about a sound, delete it.
- If a sound is unpleasant to you, delete it.
- If a sound is disrupted (say, by shuffling or airplanes), delete it.
- If a sound is distorted, delete it.
Painters add; sculptors remove. This step in the process is as sculpting: if you focus on removing sounds that do not meet your criteria or follow your rules, then the remaining sounds will.
Step 4: Apply Selection-based Processing
All samples are unique, and although global processing is effective in improving their quality generally, each can benefit specifically from tailored processing. The steps for applying selection-based processing are as follows:
- Select a region.
- Above the track header area, choose Functions > Selection-Based Processing…
- In the Selection-based Processing window, add plug-ins as you would on a channel strip, and enable a preview of the processing by clicking the preview button (volume icon).
- Press Apply.
The goal in this step is twofold: first, to remove muddiness, and second, to balance frequencies. Muddiness is usually obvious, and usually a consequence of some zealous frequency (or frequencies) below 500 hertz; however, the source of muddiness may vary both depending on and relative to the sound in question, so use your ears to identify it. If you’re unsure about what to listen for, just identify frequencies that appear overbearing or out of place, or that otherwise bother you, and then do your best to tame or remove them. The question you should be asking yourself in this step is, not “Does this sound perfect?”, but “Does this sound better?” If it sounds better, then apply the processing and move on.
💡 Use minimal necessary force when applying selection-based processing, as the purpose of this step is, not to alter sounds, but to clean and enhance them.
Step 5: Apply Channel Strip Processing
To unify your samples, apply minimal equalization and compression to the channel strip. If you want to add saturation, distortion, or effects, of course do so as well.
Step 6: Cull Again
Now that your samples are in their final forms, run through them once more. The criteria for this culling, however, should be different from the first — for example, you may search for sounds that are too similar to each other and remove the worse of them; or you may search for sounds that are simply uninteresting and remove them from the collection. Whatever you choose, be especially critical in this step, as the results of your judgements will be your final product.
Step 7: Rename
To make your samples manageable — either by you or by others — rename the samples by selecting the Text Tool from the tool menu and clicking the upper part of each region. If your samples are pitched, include the pitch in the name.
Step 8: Export
- Select all regions.
- Choose File > Export > Regions as Audio Files…
And that’s it! I hope you found this information useful, and that it enables and encourages you to create your own sounds with the tools already available to you.
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