FAQ
General
What is Chirps?
Chirps is a bioacoustics field companion for iPhone and iPad. It provides real-time, GPU-accelerated spectrogram and waveform visualisation, live audio monitoring (passthrough and heterodyne), WAV recording with iCloud sync, and high-quality spectrogram export.
Who is Chirps for?
Chirps is built for field researchers, bat surveyors, birders, nature sound recordists, and students of acoustics. It is useful for anyone who needs to visualise, monitor, or capture sound in the field without a laptop.
Does Chirps require an internet connection?
No. Chirps operates entirely offline. It makes no network connections of any kind during normal use. iCloud Drive sync uses Apple’s system APIs and operates independently of the app — Chirps itself does not connect to any external server.
Does Chirps collect any data?
No. Chirps collects no personal data, usage data, crash reports, or analytics of any kind. See the Privacy page for a full breakdown.
Audio & Hardware
What sample rates does Chirps support?
Chirps uses the sample rate negotiated by iOS for the active audio session. This is typically 44.1 kHz or 48 kHz depending on your device and the connected microphone. Higher and custom rates are supported when the connected hardware provides them and iOS exposes them. Discovered custom rates are kept with the device and shown in Settings with a Custom tag.
Can I use an external USB microphone or audio interface?
Yes. Chirps supports iOS-compatible USB microphones, audio interfaces, and soundcards connected via USB-C or Lightning. When an external input is connected, Chirps scans the route, probes supported channels and sample rates, and remembers authentic capabilities for that device. This is particularly useful for bat detection work where an ultrasonic microphone is required.
What audio file format does Chirps record?
Chirps records uncompressed PCM WAV files. The bit depth and sample rate match the active audio session configuration.
Does Chirps support Bluetooth microphones?
Bluetooth audio devices use the SCO/HFP profile for input, which limits sample rate to 8 kHz or 16 kHz. Chirps will use whatever input iOS provides, but wired USB audio is strongly recommended for meaningful frequency analysis above a few kilohertz.
Which iOS devices are supported?
Chirps runs on iPhone and iPad.
Spectrogram & Visualisation
What frequency range is displayed?
The display range extends from 0 Hz to half the active sample rate (the Nyquist frequency). At 44.1 kHz this is 0–22.05 kHz; at 48 kHz, 0–24 kHz. With a 192 kHz-capable USB microphone, the display extends to 96 kHz. Devices with higher or custom sample rates extend the range when iOS exposes those rates.
How does the dynamic range emphasis work?
Chirps applies a perceptual emphasis curve to the spectrogram colour mapping. More of the palette range is allocated to the top 30 dB of the visible signal, where acoustic detail is typically most meaningful. The colour range follows the current live ring buffer or Data Review playback window and breathes down gradually as loud transients leave view.
What is the difference between spectrogram and waveform modes?
The spectrogram shows frequency content over time — each horizontal slice is an FFT frame, colour representing amplitude at each frequency bin. The waveform shows amplitude over time as a conventional oscilloscope-style trace. Both are rendered live from the same audio stream. You can switch between them without interrupting the stream or a recording in progress.
Recording & Export
Where are recordings saved?
Recordings are written directly to the app’s local storage on your device. If iCloud Drive is enabled, files sync automatically to your iCloud Drive folder and become available on your Mac or other devices without any additional action.
How does iCloud sync work?
Chirps uses Apple’s standard iCloud Drive storage APIs. Files appear in the Chirps folder in iCloud Drive. No Chirps account or third-party cloud service is involved. Sync is handled entirely by the operating system.
Can I adjust pre-trigger duration while recording?
Yes. The pre-trigger duration can be adjusted in Settings → Recording at any time, including while the stream is running. If you change the value while a recording is already underway, the new setting takes effect for the next recording only; the start point of the recording currently being written was fixed when you tapped Record. Record becomes available only when enough buffered audio exists for the chosen pre-trigger value.
How do I export a spectrogram image?
In Data Review, open a recording, set the Window slider to Full, switch to the offline spectrogram, then single-tap the plot. A share button appears at the bottom right. Chirps renders a landscape PNG with scientific axes, ticks, grid lines, colour legend, filename, and Chirps attribution. It is suitable for reports and publications.
Monitoring
What is passthrough monitoring mode?
Passthrough monitoring routes the incoming audio signal directly to the device’s output (headphones or speaker) with minimal latency. This lets you hear what the microphone is capturing in real time while the spectrogram is running. The signal is scaled to the current device volume level to ensure that the far-field signals that are typically low amplitude are audible. Note: Due to in-built scaling, the PT monitoring may be noisier. Adjust the monitoring gain and device volume to reduce the hissing noise.
What is heterodyne monitoring mode?
Heterodyne monitoring shifts ultrasonic frequencies into the audible range by mixing the incoming signal with a tunable carrier frequency. This is the standard technique used in bat detectors. You hear a tonal buzz when an ultrasonic signal crosses the carrier frequency. Chirps implements this in software using the active audio input.
Can I tune the heterodyne frequency while listening?
Yes. The heterodyne centre frequency can be adjusted continuously while monitoring is active, without stopping the stream or muting the output. The plots continue updating in parallel.
Does Chirps support background audio streaming?
Chirps includes background streaming support, allowing the audio session to continue when the app moves to the background. Recording will continue uninterrupted if a session is in progress. When background streaming continues, Chirps sends a local reminder notification after approximately one minute.
Privacy & Permissions
Why does Chirps request microphone access?
Microphone access is required to receive audio from the device’s built-in microphone or any connected external microphone. Without this permission, the app cannot display a spectrogram or make any recordings. The permission is requested at first launch. You can review and revoke it at any time in iOS Settings → Privacy & Security → Microphone.
Is audio ever recorded without my knowledge?
No. Audio is processed only when you explicitly start the stream. Recording to disk only occurs when you explicitly start a recording. If you allow background streaming, an active stream or recording can continue after the app moves to the background, and Chirps reminds you with a local notification.
What data does Chirps collect?
None. Chirps collects no personal data, no usage analytics, no crash reports, and no device identifiers. See the Privacy page for the complete policy.
Offer Support
How can I support this project?
If you so desire, please consider a small donation via Buy Me a Coffee.
Have a question not covered here? Visit the Support page.