Pada umumnya, tiap osiloskop sudah dilengkapi sumber sinyal acuan untuk kalibrasi. Sebagai contoh, osiloskop GW tipe tertentu mempunyai acuan gelombang persegi dengan amplitudo 2V peak to peak dengan frekuensi 1 KHz.
Misalkan kanal 1 yang akan dikalibrasi, maka BNC probe dihubungkan ke terminal masukan kanal 1, seperti ditunjukkan pada gambar berikut:
Gambar di atas menggunakan probe 1X, dengan ujung probe yang merah dihubungkan ke terminal kalibrasi. Capit buaya yang hitam tidak perlu dihubungkan ke ground osiloskop karena sudah terhubung secara internal. Pada layar osiloskop akan nampak gelombang persegi. Atur tombol kontrol VOLTS/DIV dan TIME/DIV sampai diperoleh gambar yang jelas dengan amplitudo 2 V peak to peak dengan frekuensi 1 KHz., seperti ditunjukkan pada gambar berikut:
Gunakan tombol kontrol posisi vertikal V-pos untuk menggerakkan seluruh gambar dalam arah vertikal dan tombol horizontal H-pos untuk menggerakkan seluruh gambar dalam arah horizontal. Cara ini dilakukan agar letak gambar mudah dilihat dan dibaca.
Ghostly Voices From Thomas Edison’s Dolls Can Now Be Heard
Though Robin and Joan Rolfs owned two rare talking dolls manufactured by Thomas Edison’s phonograph company in 1890, they did not dare play the wax cylinder records tucked inside each one.
The Rolfses, longtime collectors of Edison phonographs, knew that if they turned the cranks on the dolls’ backs, the steel phonograph needle might damage or destroy the grooves of the hollow, ring-shaped cylinder. And so for years, the dolls sat side by side inside a display cabinet, bearers of a message from the dawn of sound recording that nobody could hear.
In 1890, Edison’s dolls were a flop; production lasted only six weeks. Children found them difficult to operate and more scary than cuddly. The recordings inside, which featured snippets of nursery rhymes, wore out quickly.
Yet sound historians say the cylinders were the first entertainment records ever made, and the young girls hired to recite the rhymes were the world’s first recording artists.
Year after year, the Rolfses asked experts if there might be a safe way to play the recordings. Then a government laboratory developed a method to play fragile records without touching them.
The technique relies on a microscope to create images of the grooves in exquisite detail. A computer approximates — with great accuracy — the sounds that would have been created by a needle moving through those grooves.
In 2014, the technology was made available for the first time outside the laboratory.
“The fear all along is that we don’t want to damage these records. We don’t want to put a stylus on them,” said Jerry Fabris, the curator of the Thomas Edison Historical Park in West Orange, N.J. “Now we have the technology to play them safely.”
Last month, the Historical Park posted online three never-before-heard Edison doll recordings, including the two from the Rolfses’ collection. “There are probably more out there, and we’re hoping people will now get them digitized,” Mr. Fabris said.
The technology, which is known as Irene (Image, Reconstruct, Erase Noise, Etc.), was developed by the particle physicist Carl Haber and the engineer Earl Cornell at Lawrence Berkeley. Irene extracts sound from cylinder and disk records. It can also reconstruct audio from recordings so badly damaged they were deemed unplayable.
“We are now hearing sounds from history that I did not expect to hear in my lifetime,” Mr. Fabris said.
The Rolfses said they were not sure what to expect in August when they carefully packed their two Edison doll cylinders, still attached to their motors, and drove from their home in Hortonville, Wis., to the National Document Conservation Center in Andover, Mass. The center had recently acquired Irene technology.
Cylinders carry sound in a spiral groove cut by a phonograph recording needle that vibrates up and down, creating a surface made of tiny hills and valleys. In the Irene set-up, a microscope perched above the shaft takes thousands of high-resolution images of small sections of the grooves.
Stitched together, the images provide a topographic map of the cylinder’s surface, charting changes in depth as small as one five-hundredth the thickness of a human hair. Pitch, volume and timbre are all encoded in the hills and valleys and the speed at which the record is played.
At the conservation center, the preservation specialist Mason Vander Lugt attached one of the cylinders to the end of a rotating shaft. Huddled around a computer screen, the Rolfses first saw the wiggly waveform generated by Irene. Then came the digital audio. The words were at first indistinct, but as Mr. Lugt filtered out more of the noise, the rhyme became clearer.
Recently, the conservation center turned up another surprise.
In 2010, the Woody Guthrie Foundation received 18 oversize phonograph disks from an anonymous donor. No one knew if any of the dirt-stained recordings featured Guthrie, but Tiffany Colannino, then the foundation’s archivist, had stored them unplayed until she heard about Irene.
Last fall, the center extracted audio from one of the records, labeled “Jam Session 9” and emailed the digital file to Ms. Colannino.
“I was just sitting in my dining room, and the next thing I know, I’m hearing Woody,” she said. In between solo performances of “Ladies Auxiliary,” “Jesus Christ,” and “Dead or Alive,” Guthrie tells jokes, offers some back story, and makes the audience laugh. “It is quintessential Guthrie,” Ms. Colannino said.
The Rolfses’ dolls are back in the display cabinet in Wisconsin. But with audio stored on several computers, they now have a permanent voice.