Autocord for Android
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All you need is an Android phone with high resolution display, running Android 8 and up.
This app is all about triggered recording, and the reason it is named "Autocord" - for "Automated Recording". For decades we have had the concept of "VOX", which stands for "voice operated switch", a switch that operates when the sound level exceeds a given threshold. It is typically used to turn on a transmitter or recorder when someone speaks and turn it off when they stop speaking, instead of a push-to-talk button on transmitters, or to save storage space on recording devices. VOX operation always had the deficiency that it triggers on any sound whatsoever, as long as it exceeds the amplitude threshold. The old VOX switching suffered from other problems besides triggering on unwanted sounds. It also chopped up speech, and users of this soon learned they needed to begin speaking with "Ah..." or "Um..." to ensure the first word wasn't lost.
Autocord goes well beyond the concept of "VOX" to provide next generation triggering. Audio capture can be triggered not only by amplitude of the signal, but also only if it falls within a desired frequency band. Thus it can even pick out a sound of interest from below the ambient noise level, a sound that could never be captured by VOX triggering. This opens up a whole new world of potential applications.
For example, suppose you are interested in capturing the call of a distant bird with a frequency that lies within the 7th or 8th octave. The nature of ambient noise is such that the lower the frequency, the higher the amplitude, ending up with the bulk of it in the first two or three octaves. The noise level in that frequency range may be considerably higher than the amplitude of the distant bird call, yet once we set the triggers to bracket the range of frequencies emitted by the bird, we may set the amplitude trigger well below the prevailing noise level and only trigger on the bird call. Then that bird call once captured can be easily separated from the noise with proper filtering in post-processing. With its awareness of the nature of ambient noise, Autocord applies prefiltering to reduce subsonic and near subsonic frequencies to remove the "mud" from the incoming audio and further reduce its influence on triggering.
Set the frequency band to that of the human voice and record notes, meetings, observations - all hands free. Autocord captures audio from a half-second before the triggering event, and continues recording for a half-second after the triggering stops to avoid choppy sound. Then each phrase spoken becomes an independent "micro-recording" in its own right. Its peak amplitude is stored internally so that each group of contiguous samples may be played back at an individually "normalized" volume level. This alone is a huge advantage. Other recorders will normalize the audio based on the greatest peak in the entire track. Then if one loud sound occurred at some point, the audio level of the entire remainder of the track will be low in comparison. Other recorders may use what is called "compression" to reduce the level of peaks on the fly, but this introduces a whole host of artifacts into the recording, making it no longer useful for things like scientific analyses. Furthermore, in any mode Autocord displays the audio spectrum of whatever sounds are occuring, and also displays the peak frequency, its magnitude, and even its musical note value from moment to moment. This gives Autocord capabilities that go well beyond the scenarios mentioned so far, opening up many other realms of audio capture.
To record a meeting, set recording to trigger when signal level is louder than ambient noise level for frequencies that fall within the range of the human voice - this all done with a single click of a button. Now place your phone on the table at a meeting. Recording will only trigger when people are speaking. On playback there will be no long silences between speakers, effectively acting as automated editing. The audio level is normalized for each individual segment of audio triggered such that for the most part, a speaker at the far end of the table will be just as loud and clear as the person seated next to the phone. Beyond that, each event is time stamped. On playback you will see exactly what time a sound event occurred, while on record you will see the duration and size of that recording as it grows in length.
If the app is set to record and the phone rings, it will automatically pause. Answer the call, and navigate back to Autocord and unpause it to capture the conversation. Only caveat here is if you are using the speakerphone, you will not capture your end of the conversation because of the echo cancellation done by the phone. If you are using ear buds, no problem! If you are not already in record mode, ask for a moment while you navigate to the app and set it to record.
Tasks such as taking notes, making assessments, doing quick surveys, taking stock to determine what needs to be reordered, making observations of cars upon rental or items to repair, charting for dental hygenists without need of an assistant, even a pathologist doing an autopsy will all benefit from hands free operation as they record their observations.
Did you ever wonder if you talk in your sleep? Set Autocord to capture sounds above ambient background only when they fall into the range of the human voice, and leave your phone recording by the bed. It will only trigger on record when you speak or snore, and ignore sounds like cars passing in the distance. You may be quite surprised by what you hear, or even the conversations that go on between couples in their sleep!
For bird watchers, the "Dawn Chorus" is one of the most inspiring moments of the day, but the birds get up well before most folk. Set Autocord to capture sounds above ambient background only when they fall into the range of bird calls, and leave your phone on the window sill or veranda overnight on record. You will only capture bird calls, and you will be delighted with the recording.
Things that go bump in the night... Whether you believe in ghosts or not, there is often much going on while you sleep. Set the phone to trigger on any sound above the ambient background level and within a frequency range of interest, and you may be quite surprised at the sounds you capture when the mice come out to play or things go bump in the night.
Do you play a musical instrument? The value of the note you are playing will be displayed when you tune your instrument to within 12.5 cents of a standard note of the Modern Even Tempered Scale. Furthermore Autocord will provide a note by note analyses of any music it hears.
Are you deaf or hard of hearing? Set Autocord into monitor mode and watch the spectral display. You will be aware of any sounds and may even learn to identify them by their spectral content.
Peak in on the evolving Help Manual for more details