Category Archives: Audio

DTMF Touchtone Telephone Tones Relating to Notes on a Piano

A Reader Asks


“Which Piano Notes do Touch-Tone Dial Frequencies Generate?”


There are 8 frequencies that, when set in an X-Y Matrix combine to produce 16 dual tones. The frequencies are set in two groups. (All frequencies are in Hz).


High Group







Low Group







The combinations and what they create are as follows:


















SIDEBAR — The letters A, B, C and D are not commonly found on your typical telephone set. They are used for special signaling and switching operations the consumer might need with special software or home equipment.


Let’s use the given that A4 is 440Hz and Middle C is 256Hz. These also happen to be standard audio calibration frequencies used for certain calibrations and setups.


Cheating a bit an equation was not used to calculate the frequency vs. musical notes. I did a comparison against some technical information I have in my Standards and Practices tech files. This will get us in the ballpark. Most of these have a tolerance of +/- 50 cents. Here is what we discover:


1209 (High side of D6)

1336 (High side of E6)

1477 (Low side of F#6)

1633 (Low side of G#6)


941 (Low side of A#5)

852 (High side of G#5)

770 (Low side of G5)

697 (Low side of F5)


As you can see the frequencies do not match musical notes exactly. This is because the frequencies were chosen by design to avoid dialing mistakes by familiar ambient sounds picked-up by the telephone’s receiver (microphone). Technically, if the frequencies matched exactly, misdialing might occur if there was music playing while one was dialing. The frequencies were also chosen so as not to interfere with other telephone tones used in the network for operations like billing, call transfers and other telemetry used to advance telephone calls. -33-




Lithium Ion Battery Air Travel Restrictions

If you are one of the many air travelers who carry spare lithium laptop, cell phone, camera and other electronic equipment batteries with you when traveling by air, take note: The government has some new rules which go into effect on New Year’s Day, 2008.


There are new regulations going into effect on January 1, 2008 if you travel by air with lithium batteries. Everyone would be well served by checking with the Transportation Security Administration (TSA) website BEFORE they travel. 


The SafeTravel.Dot.Gov website has additional information that may be helpful.


This information is subject to changes by the Federal Government. Check back with the above links often for the most up to date information. -33-


EDITOR’S NOTE – 12-30-07 at 2100H – Minor revisions to clarify article.


10 Tips For Using Wireless Microphones

Wireless microphone systems seem to be everywhere today. The spectrum is getting crowded and with the application of digital television and a plethora of other wireless gizmos frequency availability is at a premium. Knowing how to set up and use these systems is important to getting the best performance and to stay within regulations.

  1. Always use fresh batteries. Make sure batteries are installed properly matching the positive – negative prongs. Improper installation could result in shorting out the electronics, fire or in some cases the battery could explode. Make sure battery terminals are touching the battery tightly and that the battery is tightly secured in the battery holder to avoid power drop and shortage. When using more than one battery in a pack replace all batteries at the same time. Never use a fresh battery with a used battery. Avoid using rechargeable batteries unless the manufacturer designs them for use with the units.
  2. Place your receivers properly. For best reception keep receiver in a high, open area and within line-of-site of the transmitter if possible. Avoid areas with liquids, cables lines, steel or metal structure, neon lights, satellite receivers, scanners, other audio lines and cell phones that might interfere with your reception. 
  3. Optimize reception. To avoid drop out, expand the antennas as wide and far as they go. Stay within your transceiver’s recommended reception range whenever possible. Although a range test is a good suggestion before use, be aware that the system response changes with the environment and as areas fill with people and objects.
  4. Don’t pop your P’s. To avoid outside noise and vocals pops use a windscreen. For best results, a windscreen is always recommended for a headset microphone
  5. Place microphones properly. For best vocal response, keep the talent’s mouth 4-6 inches away from handheld microphone Headset microphones should be placed directly in front on the mouth within 1-3 inches. A lavaliere microphone should be placed at heart level or at 10-12 inches down from the chin. Suggest that talent wear clothing that dampens noise such as cotton and wool, avoiding noisy material such as leather, metals, satin, silk and polyester blends. 
  6. Handling the microphones. Avoid dropping the microphone, touching the microphone with wet hands, or blowing into the microphone to see if it is on. Place the microphone on your talent to avoid sweat clogging the element. When wearing a lavaliere microphone avoid contact with the chest to cut down on unwanted sounds.
  7. Don’t bang heads. Make sure your transmitter and receiver are using matching frequencies. Be aware that others may be working with wireless in proximity to yours, which may cause frequency disturbance and drop out. To solve this problem utilize a frequency agile system or a wired microphone If you don’t have a back up and others are using the same frequency in the area, keep the transmitter close to your receiver to limit problems and shut off the transmitter when not in use. 
  8. Avoid the sonic boom. When using wireless, as with any other audio products, make sure the unit is turned off and volume is down before inserting wires. Make sure volume is turned down before speaking or playing through the unit. 
  9. Hold the howl. Avoid subjecting the microphone to feedback by walking in front of speakers, placing the microphone on the floor or near power supplies or amps while the microphone is on. 
  10. Adjustments. Squelch adjustment can be used to help boost reception and frequency response.


10 Simple Suggestions For Handling CDs and DVDs

There are countless bytes of precious memories and critical data stored on optical discs every day but the average user has no idea just how sensitive the media can be. The following is an extract from the NIST’s Quick Reference Guide to optical media care. A good starting place to learn how to care for your optical media:

  1. Handle discs by the outer edge or the center hole. Do not bend the disc.
  2. Use a non-solvent-based felt-tip permanent marker to mark the label side of the disc.
  3. Keep dirt or other foreign matter from the disc.
  4. Store discs upright (book style) in plastic cases specified for CDs and DVDs.
  5. Return discs to storage cases immediately after use.
  6. Leave discs in their packaging (or cases) to minimize the effects of environmental changes.
  7. Open a recordable disc package only when you are ready to record data on that disc.
  8. Do not touch the surface of the disc or use adhesive labels.
  9. Store discs in a cool, dry, dark environment in which the air is clean. Do not expose the disks to bright sunlight for extended periods of time.
  10. Remove dirt, foreign material, fingerprints, smudges, and liquids by wiping with a clean cotton fabric in a straight line from the center of the disc toward the outer edge. Do not wipe in a direction going around the disc.


The National Institute of Standards and Technology or NIST has researched the matter and publishes several excellent references on the subject of proper care and handling of CDs and DVDs.  Following the link will direct you to the NIST Website where you will find Special Publication 500-252, October 2003, Final. This publication carries a wealth of information for use, storage and care of optical media.

There are no absolute assurances that information will always be readable on any media but much can be done to minimize data loss and the expense of recreating material lost to issues as controllable as improper storage or writing a title on the face of the disc just to name two. -33-

What’s The Buzz? Tell Me What’s Happening.

 A Reader Asks:

I notice a distinct chirping or buzzing in a defined, rhythmic pattern in the audio portion of my production. What causes this and is there anything that I can do to prevent it?

Many issues can cause chatter or noise in audio systems. Some of the most frustrating to deal with lately seem to be coming from portable wireless devices.


Cellular communication can be the source of this interference when a subscriber is using their wireless device near some speakers or poorly shielded audio cables, controls and other equipment that can resonate radio frequencies (RF). One of the biggest causes is shielding, or lack thereof. What is happening is poorly shielded gizmos can act like an antenna picking up the cell phone’s generated frequencies. At a very basic level, you are hearing someone’s telephone communication.

Some telephone networks cause more electronic noise than others because of things like, how often they communicate with devices, the frequency bands they use and how much power the device emits. 

The amount of noise caused by cell phones and networks when near sensitive audio devices is related to how efficiency the telephone communicates with the network and stays connected. Some telephones need to talk with the tower more often than others.

Experts say that the interference is an intrinsic part of cellular technology and not much can be done to prevent it. We live in a very noisy world from a radio frequency standpoint.


Solving the issue is not easy. One thing that will help is to do away with copper cabling all together and install fiber optic cable but other hardware is still open to the problem. The best way is to insist that everyone within the production’s proximity turn-off his or her cellular devices. Not set to vibrate-Power-off completely! All well and good unless you pull up your mobile production unit near an offending system’s cell site.

Part of the responsibility lies with the manufacturers to provide better shielding and systems in their own devices. Part of the responsibility lies with audio and video system installers and designers to address this problem and design-in better RF shielding to prevent or at least minimize impact.

Try This

  • Experiment with wire dress
  • Be sure all shields are soldered
  • Use quality cable.
  • Use quality connectors 
  • Maintain a totally balanced audio system
  • Have a good maintenance program -33-