Why Do Cell Phone/Telephone Microphones Sound So Bad?


There is seemingly no end to the things you can do on your cell phone today. In fact, some people earn their entire living by logging into and posting on smartphone apps. Yet, for all of this technological advancement, it still seems that the most basic function of a cell phone—to place a call—is underwhelming due to bad microphone sound quality. Why is this the case?

Why do cell phone/telephone microphones sound so bad? The sound quality on cell phones is poor due to their small, omnidirectional microphones that must be operated within strict confines for “optimal” sound quality. It is possible that sound quality could improve using specialized directional microphones, but users would have to give up a few features on their device.

While the quality of cell phone microphones may leave a lot to be desired compared to professional studio microphones, they actually do an amazing job considering the design restraints. Below, we’ll cover the reasons why cell phone microphones have poor sound quality and the options users have to improve it.


A Brief History On Telephone Sound Quality

The range of human hearing is widely accepted to be between 20 Hz and 20,000 Hz while the range of the human voice, in general cases, will range between roughly 80 Hz and 14,000 Hz.

In the early days of telephone audio transmission, the audio signals transmitted over telephone lines were band-passed in what is known as the “Voiceband” or “Narrowband”. This effectively filtered out all audio frequencies outside the range of 300 – 3,400 Hz. Using this band, much of the speech intelligibility could be transmitted with rather low signal information, allowing for easier transmission.

For more information on band-pass filters, check out my article Audio EQ: What Is A Band-Pass Filter & How Do BPFs Work?

As technology advanced and further studies were conducted on the harmonic contents of human speech, the Wideband (50 Hz – 7,000 Hz) was developed and, later, the Superwideband (50 Hz – 14,000 Hz).

Today, some cell phone standards utilize Wideband “HD Voice” codecs, though many transmission standards continue using the relatively low-information “toll quality” Narrowband. 

This confine, along with mass-production of cost-affordable microphones and audio circuits, plays a huge role in determining the overall audio quality of telephone/cell phone audio.

Interference and other transmission issues will also affect the audio quality of such phones.

So, then, with these limitations, there’s really no need for a high-end studio-grade microphone, anyway. That being said, let’s move on with this article to better understand why telephone/cell phone microphones sound so bad.


Causes Of Poor Sound Quality In Cell Phone Microphones

Cell phones use small, omnidirectional electret condenser microphones or confined in less-than-ideal housings or MEMS microphones. These minute microphones are designed to operate under very little power and fit nicely into the cell phone’s circuitry. 

Related article: What Kind Of Microphones Are Used In Cell Phones?

As an omnidirectional microphone, they are capable of picking up sound equally from all directions. This works great when the only sound is that of your voice. However, when the microphone detects other strong sounds, such as heavy winds or loud music, coming from another direction, your voice can become lost in an assortment of noise.

For more information on electret condenser microphones and the omnidirectional polar pattern, consider reading the following My New Microphone articles:
The Complete Guide To Electret Condenser Microphones
What Is A Condenser Microphone? (Detailed Answer + Examples)
What Is An Omnidirectional Microphone? (Polar Pattern + Mic Examples)

To expand on this, a few other factors may cause poor results in a cell phone microphone. 

Distance From Microphone

Cell phones are engineered to expect the speaker to be a certain distance away from the microphone. For example, when the phone is in handset mode, it expects that the phone will be held next to the speaker’s face. When it is in hands-free mode, it expects the microphone to be about 25 centimetres away from the speaker’s face.

When these distances are compromised, the microphone will not function as intended. If you slide the phone too far down your face when talking, it may sound like you are talking from the bottom of the barrel. If you are too far away from the microphone in hands-free mode, it may detect a closer sound source as the dominant recording input. 

Frequency Of Speaking

Just as cell phone microphones are engineered with certain distances in mind, so too are they designed to expect to record the frequency of a normal human voice. The microphone will do its best recording when you talk in a normal voice range. 

Many users are tempted to raise their voice and start talking forcefully directly into the microphone when they realize that the receiver is not hearing them well, but this can actually lead to increased distortion and cause the quality of the sound to worsen.

Limited Fidelity Capacity

Audio fidelity refers to how accurately an audio signal reproduces its source. So, in the case of cell phone microphones, the fidelity would be measured by how accurately the voice heard by the receiver reflects what you actually sound like. When dealing with cell phone microphones, their minuscule size and cheap materials limit the fidelity that can be achieved. 

Cell phone carriers use software known as codecs to take the recorded sound from the microphone, store it digitally, and transmit it back to sound via the receiver’s speaker. The advanced multi-rate codecs used by most cell phone carriers top out at 12.2 kilobits, limiting the amount of fidelity that can be achieved when storing sound digitally. This ties back into the transmission issues mentioned in the second A Brief History On Telephone Sound Quality.

Microphone Obstructions

While the small size of the omnidirectional microphone limits cell phone audio quality, there is a chance that the microphone itself is not causing the issues and that dust or other buildup is blocking the audio intake. 

Check the microphone intake and see if there is any visible blockage. The microphone intake is located along the bottom edge of the phone and will usually consist of five or six dots or dashes in a row. Take a small toothbrush and gently clean away any buildup. If the cell phone is in a protective case, remove the phone from the case and clean the case’s interior to ensure that there are no obstructions on that end.

While dust buildup may affect the audio intake and worsen the quality of the sound, the microphone itself is typically protected by a fine, mesh-like membrane that prevents foreign particles from entering the phone’s interior. If a grain of dirt or sand were to somehow bypass this membrane, a larger issue would be at hand that could require a replacement of the microphone altogether. 

Issues With The Sound Transmission Process

The microphone recording your voice is just one step in the sound transmission process. The typical journey of sound from sender to receiver goes something like this:

  1. Sound waves travel from your mouth to the microphone.
  2. The microphone converts these sound waves into an electrical signal.
  3. Your carrier’s codec converts the electrical signal to a digital signal.
  4. The digital signal is processed, compressed, and transmitted to the receiver.
  5. The receiver converts the compressed digital signal back to an electrical signal.
  6. The electrical signal is converted by the speaker back into sound waves.

As you can see, even in this simplest of scenarios, there is a lot that can go wrong that is not necessarily the fault of the microphone. Throw in Bluetooth, which adds an additional layer of conversion and transmission, and even the highest-quality microphones will likely experience some kind amount of distortion.


Why Not Switch To Directional Microphones?

The omnidirectional microphones used in cell phones can provide poor sound quality when recording conditions are not ideal. This may leave you wondering why cell phone engineers don’t convert to a directional microphone to channel and transmit the human voice more effectively. After all, directional microphones, such as cardioids, hypercardioids, and supercardioids more effectively reject ambient noise than omnidirectional microphones.

To learn more about these directional microphone polar patterns, check out the following My New Microphone articles:
What Is A Cardioid Microphone? (Polar Pattern + Mic Examples)
What Is A Hypercardioid Microphone? (Polar Pattern + Mic Examples)
What Is A Supercardioid Microphone? (Polar Pattern + Mic Examples)

There are a few reasons why directional microphones do not make a good choice for cell phones:

  • Although they do a good job of blocking out ambient noise, there is very little placement flexibility when working with directional microphones. If the microphone is not properly situated, the microphone can actually block out the speaker’s voice. Low-quality sounds from an omnidirectional microphone are better than no sound at all.
  • It is important to remember that voice recordings are only one function of the modern cell phone/smartphone. A directional microphone would not be a strong choice for recording live events in which you want to capture all sounds or use sound recognition apps such as Shazam. 

Conclusion

With all of the advances in cell phone technology, it is a bit frustrating that something as basic as a phone call can be a bit underwhelming due to the poor recording quality of the cell phone microphone. 

While the cause of the inferior sound stems largely from the small size of the cell phone’s omnidirectional microphone that must be used within strict confines for optimal functionality, there are secondary issues, such as a dirty audio intake or issues with the sound transmission process, that could be negatively impacting sound quality, as well.


Does a microphone change your voice? Microphones, like all audio equipment, will alter the sound of your voice. Some microphones capture voice more accurately than others, but all do alter sound in one way or another. On top of that, the way you hear your own voice is different than the way your voice actually sounds.

Related article: Does A Microphone Change Your Voice? (Natural Hearing Vs. Playback).

How do I reduce microphone noise? There are plenty of noise sources that can add unwanted noise to a microphone signal. Luckily, there are methods of reducing the noise cause by nearly every one of these sources. Here are just 15 methods to reduce microphone noise:

  1. Choose A Condenser Or Active Mic With Low Self-Noise
  2. Choose A Dynamic Mic With A Humbucking Coil
  3. Place Mics Closer To The Sound Source
  4. Use A Shock Mount
  5. Use A Pop Filter
  6. Record In Quiet Or Soundproof Environments
  7. Use Balanced Mic Cables
  8. Do Not Run Mic Cables Alongside Power Cables
  9. Use An RF Filter
  10. High-Pass Filter The Mic Signal
  11. Use A Pad When Approaching Max SPL
  12. Plug The Mic Into A Mic Input
  13. Use Clean Preamps
  14. Use An In-Line Preamp Before The Mic Preamp
  15. Use A Noise Suppression Plugin In Your DAW

To learn more, check out my article 15 Ways To Effectively Reduce Microphone Noise.

Arthur

Arthur is the owner of Fox Media Tech and author of My New Microphone. He's an audio engineer by trade and works on contract in his home country of Canada. When not blogging on MNM, he's likely hiking outdoors and blogging at Hikers' Movement (hikersmovement.com) or composing music for media. Check out his Pond5 and AudioJungle accounts.

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