How conventional hearing aids work
Sound enters the hearing aid through the microphone which converts sound waves into an electrical current.  This current is amplified through an electronic circuit made up of  transistors, capacitors and resistors.  The amplified current then is converted back into sound using a loudspeaker.
The circuit of a conventional hearing aid contains hundreds of microscopic electronic components.  This electronic prescription is customized to correct a particular impairment.

Sound must be amplified only for pitches affected by the ss. The prescription in a conventional aid is hardwired into the circuit.  If the prescription needs to be changed, the components within the aid must be replaced.

WHAT DOES "DIGITAL " MEAN?
Digital means that the hearing aid has a computer inside it. The computer contains the instructions, or "program" that tells the hearing aid how to amplify sound.  Computer control of sound enables it to be processed in more complex ways than are possible before digital technology.
WHAT DOES "PROGRAMMABLE" MEAN?
The prescription within a programmable aid is stored in the aid's computer.  Programmable means that the prescription can be changed or reprogrammed easily in the office without changing the whole hearing aid.

ADVANTAGES OF DIGITAL-PROGRAMMABLE HEARING AIDS

Higher fidelity: Digital-programmable aids can amplify a wider range of frequencies without the distortion usually, found in conventional aids.  Thus, digital hearing aids usually sound clearer, especially in difficult, noise, environments.
Less feedback: Digital hearing aids do not squeal as much as conventional aids. Multiple programs.  The way a hearing aid amplifies sound in one environment (e.g.,quiet) may not be ideal for hearing in other environments (e.g., noise).  Multiple programs enable a patient to choose the prescription that is most effective for hearing in a particular situation - at the press of a button.  This is like
having two hearing aids in one.
Flexible: Because the prescription of a digital aid is so easily altered by your audiologist, if your hearing should change, the prescription also can be changed by reprogramming the aid. This flexibility also allows your audiologist to fine-tune the aid better when adjusting it within the trial period.
More comfortable: Digital hearing aids can be programmed so that sound never exceeds a patient's tolerance for loud sound.
More precise: Digital aids can be adjusted more precise conventional aids so that the right amount of amplification is delivered to the ear.