The internal clock drifts away from true whether it is idle or recording, powered on or off.

• Different recorders' clocks drift at different rates from one another and from other time-stamping data collection equipment such as video cameras.
• In old-style devices (serial numbers <20000), the internal clock is powered by a separate battery from the main battery for the unit.

If LENA Pro can read the recorder's clock, the clock will be evaluated and synced upon connection, according to the following rules - whether or not the device contains data:

• If the difference is <1 minute, no adjustment is made.
• If the difference is >1 minute but <15 minutes, the clock adjustment happens silently.
• If the difference is >15 minutes, the software prompts the user to adjust the clock (on the premise that a clock may be that far off on purpose).

If the computer cannot access the clock, you will see the message “Unable to verify DLP clock time” and a prompt to disconnect and reconnect the DLP (recorder).  This message indicates that the software can neither read nor adjust the clock time on the recorder.

Each recording is stamped with the clock time as it reads when REC is pressed, not when the recording is uploaded.  

• If the device does contain data when it is synced, the existing stamp on that recording is not altered in the sync.  
• The sync prepares the device for the next recording.  
• To minimize the difference between a recording's starting time stamp and the real time, minimize the lag between syncing and recording.
  • If your recorders have sat idle for a long time, you should connect them to the software prior to sending them out to record audio.

Old-style recorders

Although the clock will still drift over time, recorder firmware versions 2.18+ continuously adjust the processor's sampling rate during recording to match the recorder's clock time as closely as possible.

The adjustments minimize how far ahead/behind of “real time” the "recording time" can get over the course of a full day of data collection.

Keeping recording time in line with clock time eliminates some audio processing failures, and allows researchers to more confidently correlate LENA data timestamps with data from other equipment used in IRB-approved investigations, such as video, sleep study data, stress marker measurements, or geo-location data.  However, the LENA recorder data cannot be expected to sync perfectly with any external device, including another LENA recorder.  It was not designed to sync with external devices; its sole purpose is to collect audio for analysis by the LENA algorithms.  

Note that because LENA Pro does not adjust a clock that is within 1 minute of the computer's time, the only way to ensure approximate alignment of two recorders' clocks (to the second) at the start of a recording is to first be sure they are both off by more than a minute when connected to the LENA Pro computer, and to do this immediately before initiating a recording.

New-style recorders

Devices with serial numbers 20000 and above experience less clock drift and the processor and clock stay aligned.