To parents, a baby's cry is a signal of hunger, pain, or discomfort.
But to scientists, the subtle acoustic features of a cry, many of them imperceptible to the human ear, can hold important information about a baby's health.
Now a team of researchers from Brown University and Women & Infants Hospital of Rhode Island in the US have developed a new computer-based tool to perform finely tuned acoustic analyses of babies' cries.
"The idea is that cry can be a window into the brain," said Barry Lester, director of Brown's Centre for the Study of Children at Risk.
The team hopes their baby cry analyser will lead to new ways for researchers and clinicians to use cry in identifying children with neurological problems or developmental disorders.
"There are lots of conditions that might manifest in differences in cry acoustics," said Stephen Sheinkopf, assistant professor of psychiatry and human behaviour at Brown, who helped develop the new tool.
"For instance, babies with birth trauma or brain injury as a result of complications in pregnancy or birth or babies who are extremely premature can have ongoing medical effects. Cry analysis can be a non invasive way to get a measurement of these disruptions in the neurobiological and neurobehavioral systems in very young babies."
The new analyser is the result of a two-year collaboration between faculty and hospital-based faculty at Women & Infants Hospital.
A paper describing the tool is published in the Journal of Speech, Language and Hearing Research.
The system operates in two phases. During the first phase, the analyser separates recorded cries into 12.5-millisecond frames. Each frame is analysed for several parameters, including frequency characteristics, voicing, and acoustic volume.
The second phase uses data from the first to give a broader view of the cry and reduces the number of parameters to those that are most useful. The frames are put back together and characterised either as an utterance - a single cry - or silence, the pause between utterances.
Longer utterances are separated from shorter ones and the time between utterances is recorded. Pitch, including the contour of pitch over time, and other variables can then be averaged across each utterance.
In the end, the system evaluates for 80 different parameters, each of which could hold clues about a baby's health.
"It's a comprehensive tool for getting as much important stuff out of a baby cry that we can," said Harvey Silverman, professor of engineering and director of Brown's Laboratory for Engineering Man/Machine Systems.
If neurological deficits change the way babies are able to control their vocal chords, those tiny differences might manifest themselves in differences in pitch and other acoustic features, they believe.
"Cry is an early warning sign that can be used in the context of looking at the whole baby," Mr Lester said.
The automated analyser enables researchers to evaluate cries much more quickly and in much greater detail than previous tools.
The team plan to make it available to researchers around the world in the hopes of developing new avenues of cry research.
Professor Sheinkopf, who specialises in developmental disorders, plans to use the tool to look for cry features that might correlate with autism.
"We've known for a long time that older individuals with autism produce sounds or vocalisations that are unusual or atypical," he said.
"So vocalisations in babies have been discussed as being useful in developing early identification tools for autism. That's been a major challenge. How do you find signs of autism in infancy?"
The answer could be encoded in a cry.
"Early detection of developmental disorders is critical,” Mr Lester added. "It can lead to insights into the causes of these disorders and interventions to prevent or reduce the severity of impairment."