Sound Synthesis II: Extracting Harmonics

Analysis file:

InputSoundFile trumpet-c4.wav OutputSmsFile trumpet-c4.sms SineModel 1 nSines 1 LowestPitch 200 HighestPitch 300

Synthesis file:

InputSmsFile trumpet-c4.sms OutputSoundFile trumpet1.wav Type 1

Here is a description of parameters used in the analysis/synthesis score-files:

SineModel	Specify harmonic (1) or non-harmonic (2) analysis. (Default is harmonic analysis).
nSines	This parameter specifies the number of harmonics to analyze (when SineMode = 1).
LowestPitch	This parameter specifies the lowest pitch to search for in the input soundfile.
HighestPitch	This parameter specifies the highest pitch in Hz to search for in the input soundfile.
Type	This parameter specifies type of synthesis. Type 1 means only synthesize the deterministic part (sinewaves) of the analysis.

The pitch of the trumpet note is about 260 Hz, so the LowestPitch was set to 200 Hz and the HighestPitch was set to 300 Hz. These parameters may or may not be necessary depending accuracy of detecting the fundamental frequency on the input sound. For the case of the trumpet sound, the identification quality for the third harmonic improved when the pitch range was limited.

Now extract the first two harmonics of the trumpet note with the following analysis/synthesis files:

Analysis file:

InputSoundFile trumpet-c4.wav OutputSmsFile trumpet-c4.sms SineModel 1 nSines 2 LowestPitch 200 HighestPitch 300

Synthesis file:

InputSmsFile trumpet-c4.sms OutputSoundFile trumpet1-2.wav Type 1

Notice that the only change in the analysis/synthesis files is to change nSines from 1 to 2. Now the resynthesis extracts the first two harmonics of the trumpet sound.

To hear the second partial by itself, you can use the subtract command to remove the first harmonic from the sound of the first two harmonics:

   subtract trumpet1-2.wav trumpet1.wav trumpet2.wav

To make the extraction of harmonics from a sound less tedious, here is a command you can use to extract the lowest harmonics from a soundfile:

   smsHarmonics 1 trumpet-c4.wav trumpet1.wav

   smsHarmonics 2 trumpet-c4.wav trumpet1-2.wav

Here is a table of the first 32 harmonics of the trumpet note:

1    (1, 1n)
1-2  (2, 2n)
1-3  (3, 3n)
1-4  (4, 4n)
1-5  (5, 5n)
1-6  (6, 6n)
1-7  (7, 7n)
1-8  (8, 8n)

1-9  (9, 9n)
1-10(10, 10n)
1-11(11, 11n)
1-12(12, 12n)
1-13(13, 13n)
1-14(14, 14n)
1-15(15, 15n)
1-16(16, 16n)

1-17(17, 17n)
1-18(18, 18n)
1-19(19, 19n)
1-20(20, 20n)
1-21(21, 21n)
1-22(22, 22n)
1-23(23, 23n)
1-24(24, 24n)

1-25(25, 25n)
1-26(26, 26n)
1-27(27, 27n)
1-28(28, 28n)
1-29(29, 29n)
1-30(30, 30n)
1-31(31, 31n)
1-32(32, 32n)

Here is a soundfile which plays each of the harmonics successively: trumpetharmonics.wav.

Exercises

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1. Extract the first seven harmonics from a pitched sound of your choice. You can look through the sounds on mambo in the directory /usr/local/sms/sounds, or view the SMS example sounds on the web. Also, you can try some of the Musical Instrument Samples from the University of Iowa Electronic Music Studios which were recorded in an anechoic chamber to reduce reverberation (which will give the best results for analysis).
   
   
2. Measure the loudness of each harmonic in the sound you have chosen. Use the sndpower command available on mambo to measure the average decibel level for each harmonic. For example, the trumpet sound above has this average amplitude for each harmonic of the first seven harmonics:

   harmonic frequency loudness (decibel) amplitude 1 C4 (260 Hz) 0 dB 0.0105519 2 C5 (520 Hz) 7 dB 0.0220180 3 G5 (780 Hz) 12 dB 0.0389151 4 C6 (1040 Hz) 15 dB 0.0535522 5 E6 (1300 Hz) 10 dB 0.0315712 6 G6 (1560 Hz) 15 dB 0.0532884 7 B-flat6 (1820 Hz) 10.5 dB 0.0325092

   
   
   
3. Extra Credit: Synthesize a synthetic instrument sound using additive synthesis with the average loudness of the first seven harmonics. For example, here is the additive synthesis version of the trumpet sound: trumpetadd.wav created with the command (on mambo):

      addsyn trumpet.addsyn trumpetadd.wav
   

   Compare this sound to the real trumpet's first seven harmonics: trumpet1-7.wav. Describe both sounds and how they are similar and/or dissimilar.
   
   
4. Remix the harmonics in different amounts (for example add the 1st, 3rd, 5th, and 7th harmonics together to create a clarinet-like variation of the instrument). Make a note of interesting harmonic mixtures. Here is an example using the addsnd program on mambo which mixes the odd harmoics up to harmonic 31:

      addsnd trumpet[13579].wav trumpet[123][13579].wav trumpetodd.wav
   

5. Remove the 1st harmonic from the original sound. Does the pitch change? (It should not) Remove the 1st and 2nd harmonics from the original sound. Does the pitch change? (It probably should not) How many harmonics must be removed before the pitch changes?
   
   
6. Extra Credit: How few harmonics can be played yet still allow you to identify the instrument being played? For example, can you identify the trumpet from only the fundamental? from only the first 2 harmonics? At what point does the instrument become recognizable? Find the minimum that you need in order to identify the instrument. Then play that sound for someone else who has not been listening to the noise you have been making. Can they also recognize the sound?