Year: 2006

Wikipedia says the human voice frequency for speech is between 85 to 155 Hz for men, and 165 to 255 Hz for women. That set me thinking.

1. What is the limit to our hearing?
2. How do sounds differ?
3. How can we synthesise speech?

What are the limits to our hearing?

Kids can hear frequencies from 20 Hz to 20 kHz, while adults hear only up to 12-14 kHz (Frequency Range of Human Hearing).

To check the lower frequency limit, I created an MP3 with sounds from 1 Hz to 100 Hz at 1 second intervals. Just play the sound, and see when you start hearing something. (Of course, whether you can hear something also depends on the volume of your speaker, the ambient noise, etc.) I could hear nothing for the first 40 seconds: so I can’t hear frequencies lower than 40 Hz.

PS: Don’t be worried if you don’t hear anything for a while. You’re not supposed to! Keep the volume at full level, though.

To check the upper frequency limit, I created this MP3 with sounds from 1 kHz to 20 kHz in 1 second intervals. Just play the sound, and see when you stop hearing anything. I couldn’t hear anything beyond 14 seconds: so I can’t hear frequencies beyond 14 kHz.

How do sounds differ?

I took this audio file of someone reciting vowels and plotted a spectrogram (below). A spectrogram plots time on the X axis and frequency on the Y-axis.

Some observations:

• All the vowels have evenly spaced bars. (In this case, they’re all multiples of something around 120 Hz.)
• ‘u’ has the lowest frequency mix. ‘a’ spans from low to high. ‘i’ has a bit of low and a bit of high, nothing in the middle. ‘ai’ and ‘au’ look like ‘a’ followed by ‘i’ and ‘u’ respectively.

How can we synthesise speech?

I don’t know. There are lots of speech synthesizers. They sound robotic. I’m trying to see if knowing what sounds look like improves things. I’ll let you know if I do well.

When you make a link, there’s no guarantee that the link will work 5 years later. Sites change their URL structure. I’m finding that many of my blog entries from 2000 are invalid.

Sometimes you want to link to a concept rather than a site. In such cases, it’s better to link to a Google query.

For example, rather than link to a site that defines SVG, I could link to the Google search define:SVG.

Rather than link to a tutorial on Excel array formulas, I could link to the Google search excel array formulas. I could even link to the first hit on Google for excel array formulas, mimicking the “I’m feeling lucky” button. This may change over time, but 5 years from now, it’ll still point to the most relevant link.

To link to the Google query for “excel array formulas”, just link to the URL http://www.google.com/search?q=excel+array+formulas. To link directly to the first result, add &btnI=I'm+Feeling+Lucky to the URL. (Linking to A9 is simpler: http://a9.com/excel+array+formulas)

PS: An alternative is to link to a permanent copy of the page from the Wayback machine (it has copies of my page all the way from May 2001 to Mar 2005). (You can’t use Google’s cache. When the site changes, the cache will soon change. But it’s a good defence against site downtime. Manually doing this is a lot of effort. Ideally, future browsers will automatically take you to the Wayback machine or the Google cache. (The Firefox plugins ErrorZilla and CacheIt come close.)