Format of Audio Files

The audio files produced in Survey Solutions (audio audit files and answers to audio questions) are recorded using AAC (Advanced Audio Coding) and have a file extension .m4a.

The quality of the audio recording in web interviews (in a web browser) is fixed at:

128kbps, mono, 48kHz

The quality of the audio recorded on a mobile device (in Interviewer App) is determined by the Audio recording quality setting in the Devices tab of the workspace settings. The possible values are:

32kbps, mono, 16kHz;
64kbps, mono, 22.05kHz;
64kbps, mono, 44.1kHz;
128kbps, stereo, 44.1kHz;
128kbps, stereo, 48kHz.

Once this setting is changed, it becomes effective immediately (no need for the administrator to save or apply it), but interviewer’s devices need to receive the new setting for it to be used for subsequent recordings. This will be transmitted during the next device synchronization session.

To calculate approximate size of the audio recording (in MB) use the following formula: (B*D)/(8*1024*1024), where B is the bitrate (from the above list), and D is the duration of the audio recording in seconds.

The following table shows approximate size (in MB) of audio recording by duration and applicable bitrates:

Duration, min	Bitrate, kbps
	32	64	128
3	0.7	1.4	2.7
15	3.4	6.9	13.7
20	4.6	9.2	18.3
30	6.9	13.7	27.5
40	9.2	18.3	36.6
60	13.7	27.5	54.9
90	20.6	41.2	82.4
120	27.5	54.9	109.9

Note:

Audio recording settings are used at the recording time. If the setting is changed after the recording has been submitted to the server it will still appear in the exported data with the audio quality effective at the time when the recording was made.

Survey Solutions prior to version 26.07 utilized the 64kbps, mono, 44.1kHz format for audio recording and this format is set by default for new workspaces.

More information

See:

audio question for a description of audio questions.
audio audit for a description of the audio audit.
audio audit files for explanation in the naming of the audio audit files.