Pitch and Frequency of Human Voices

Every voice has its own unique sound, just like Amitabh Bachchan’s deep and powerful voice or Taylor Swift’s soft and high one. Just like musical instruments, our voices can produce a range of notes or pitches. In Indian music, these notes are known as Sa, Re, Ga, Ma, Pa, Dha, Ni, Sa′. Great singers like Lata Mangeshkar and Kishore Kumar are known for their wide pitch range, as they could comfortably sing from a low Sa to a much higher Sa′.

In this activity, you’ll explore how pitch changes as you move from Sa to Sa′ and see how the range of frequencies varies between different people. You’ll get to see your voice as sound waves on your phone using a frequency analyzer app like Spectroid.

Science Involved

Each musical note corresponds to a particular frequency. In Indian classical music, Sa is the base note, and as you move up to Re, Ga, Ma, and so on, the frequency increases. The top Sa′ (higher Sa) has roughly double the frequency of the lower Sa. Indian music follows a system called the saptak (meaning seven notes). These notes are not fixed to specific frequencies like in Western music. The singer chooses a starting Sa that fits their voice, and all other notes are based on that.

The sound is produced in the voice box (larynx), where the vocal cords act like stretched strings. When you sing or speak, your vocal cords vibrate, and the frequency of vibration of the vocal cords determines the pitch of your voice. Faster vibrations create a higher pitch, while slower vibrations create a lower pitch.

Several factors affect how the vocal cords vibrate:

• Length and thickness of the vocal cords: Longer and thicker cords produce a lower pitch.

• Tension in the vocal cords: Tighter cords vibrate faster and produce a higher pitch.

• Age and gender: These can also influence vocal cord size and flexibility, leading to differences in voice range.

Because of these factors, everyone’s voice is unique. Some can easily sing high notes, while others are more comfortable with deeper tones.

Activity

Requirements

Mobile phone with Spectroid app and a quiet room.

Getting Ready

Before you start, check these basic settings in the Spectroid app. You can try adjusting them during the activity to see how the spectrogram changes.

1. FFT size: This controls how clearly you can see the frequency lines. Larger values make the lines sharper. Choose a value like 4096 or 8192.

2. Frequency axis scale (Linear vs Logarithmic): In Linear view, all frequencies are spaced evenly, which makes the harmonic pattern easy to compare, but the lower frequencies get crowded and the base frequency and formants become harder to see. In logarithmic view, the lower frequencies are stretched out, and the higher ones are squeezed together. This makes the base frequency and formants easier to spot, although the spacing between harmonics becomes less at higher frequencies. For this activity, choose Logarithmic view.

3. Peak markers: Peak markers label the strongest frequencies so you can read their values quickly. For this activity, select to show only 1 marker.

Leave all other settings, including Sampling Rate, Decimations, Window Function, and Transform Interval, etc. at their default values.

Procedure

Part 1: Frequency Range

1. Sit in a quiet place where the background noise low and open the Spectroid app on your phone.

2. Hold the phone about 15-20 cm from your mouth and sing or hum the note Sa.

3. Watch the display. When you sing Sa, the sound contains the base (main) frequency along with higher harmonics. On the screen, you’ll see many peaks or bright lines. The base frequency is the lowest-frequency peak or bright line (the one closest to the left side). Record its value in hertz. The peaks at higher frequencies and the brighter lines and a higher frequency are all harmonics. They are whole-number multiples (2×, 3×, 4×, …) of the base frequency, not different notes.

   

4. Repeat the same for Re, Ga, Ma, Pa, Dha, Ni, and Sa′. Write all your readings in a table.

5. After recording Sa′, try going higher by singing into the next octave (keep sliding up above Sa′) and find the highest comfortable pitch you can reach. Stop immediately if your throat feels strained or sore.

6. If possible, repeat the above steps with other volunteers across different age groups and genders.

Part 2: Tone, Style and Frequency

1. Say a simple phrase, such as “Hello, my name is …” or read aloud a line of text in your normal speaking voice and note the range of frequencies produced.

2. Say the same phrase again in different tones – happy, angry, or sad – and observe how the frequency pattern changes with each emotion.

3. Try saying the same sentence in different styles - whispering, shouting, or humming – and observe how the pattern and range of frequencies change with each style.

4. Try speaking the same sentence with a handkerchief held loosely over your mouth. Observe how the peaks in the spectrum change. Are the frequencies still the same, or does the sound just become softer and less clear?

Observations

Part 1

Part 2

Reflect and Discuss

1. How does the frequency change as you move from Sa to Sa′?

2. Children’s voices (around 8-12 years old) often show frequencies around 300-400 Hz, adult female voices around 200-300 Hz, and adult male voices around 100-150 Hz. Teenagers fall anywhere in between these ranges, depending on how much their voices have changed. Use your data to see if your results match this pattern.

3. What factors do you think affect a person’s ability to reach high notes?

4. Explain why it’s harder to recognize someone’s voice when they are whispering?