I just met my goal for July yesterday. I added some orchestral samples and musique concrete to Landscape 7: Mountains. I had a Musiversal reading on July 16th, which went very well. One of my goals for the next couple of weeks is to mix the audio files from that session. I leave you with the updated version of Landscape 7: Mountains.
Landscapes Update: July 5th, 2020
I met my June goals, revising the pedal steel part in phrase four of Landscape 6: Beach. I also recorded a synth part for Landscape 5: Marsh on a Moog Mother 32. The goal for July is to revise Landscape 7: Mountains. I also have a Musiversal recording session on July 16th to have an orchestral part for Landscape 10: Rocky Coast. Musiversal has changed the instrumentation of their basic, now called studio, orchestra. They’ve dropped two French horns, going down to two, but added harp and percussion, so I’m excited that there’ll be harp and timpani in the next recording. For this month I’ll leave you with the latest realization of Landscape 5: Marsh, including the new synth part.
Landscapes Update: June 6th, 2020
I’ve met my goals for May. I revised the piano part of the eighth phrase of Landscape 5: Marsh. I also recorded harmonica parts for Landscape 8: Palm Glade. The goal for June is to revise Landscape 6: Beach. I also hope to do a little bit of recording in this month (maybe a synthesizer part). I have also spent some of my stimulus money contracting with Musiversal for a July recording session for an orchestral part to Landscape 10: Rocky Coast. This month I’ll leave you with a realization of Landscape 6: Beach that includes a cello part performed by Nara Shahbazyan.
Landscapes Update: May 3rd, 2020
April has been fairly productive. My revisions for this month entailed a musique concrete part to Landscape 4: Sand Dunes. This concrete part is based upon horn recordings from Landscape 7: Mountains, as well as bass harmonica and string recordings from Landscape 4. So, without further ado, I present the updated version of Landscape 4.
Landscapes Update: April 5th, 2020
What a crazy time it has been. Even in bad times there can be silver linings. Practicing self isolation I have found more time to compose and record. In March I revised the piano part of phrase two of Landscape 3: Pond, as well as the last measure of the piano part. I also found the the time to record the bass part for Landscape 8: Palm Glade, which will be included below. In April I hope to add a music concrete part to Landscape 4: Sand Dunes. Anyway, here’s the current realization of Landscape 8: Palm Glade with Carl Bugbee playing the guitar part, and me playing the bass part.
Landscapes Update: March 1st, 2020
During the month of February I rewrote the third phrase of the pedal steel part for Landscape 2: Snow. I unfortunately did not have any time to record any new tracks for the project. I do plan on recording a bass part over spring break. I do have some updated audio to share this month. Appropriately enough it is Landscape 2: Snow. This realization includes a guitar part performed by Carl Bugbee of the prominent Rhode Island cover band Take it to the Bridge, and the cello part is played by Dr. Nara Shahbazyan who performs in the Providence based New Music group Ensemble Parallax.
Landscapes Update: February 1st, 2020
During January I revised Landscape 1: Forest by adding a musique concrete layer. The sound sources I used include horn recordings from Landscape 7: Mountains, as well as bass harmonica recordings from Landscape 4: Sand Dunes. In all cases, I used Audacity to change the pitch level, as well as to stretch out the samples. My plans for February include revising the pedal steel part for Landscape 2: Snow. I’ll leave you with an updated realization of Landscape 1: Forest, including the new musique concrete layer.
Feedback in FM Synthesis
FM Synthesis can be difficult to understand. Those of us who spent time programming a Yamaha DX7, the leading FM synthesizer of the 1980s, also know how confusing it can be to program. Fortunately for those who are nostalgic for classic synthesizers of the 1980s Digital Suburban develed Dexed, a DX7 emulator.
The good news is that Dexed works just like a DX7, allowing you to port over classic patches. The bad news is that Dexed works just like a DX7, in that it can still be confusing and awkward to program. However, the better you understand FM synthesis, the better equipped you’ll be to tackle Dexed.
In this post we’ll investigate feedback, which in FM synthesis is when some of the output an operator is fed back to modulate itself. In a DX7, there are eight levels of feedback available (0-7 inclusive). No feedback is present at level 0, while at level 7 there is (presumably) 100% feedback.
I tested feedback in Dexed by using algorithm 32, which is the only algorithm in which a carrier modulates itself. I turned off all the operators except for operator six, which is set at full volume, and at a ratio of 1.00 (the first harmonic). Each pitch is at A4 (440Hz) with full velocity.
It is interesting to see and hear the results of the test. Predictably at feedback level 0 a simple sine wave results. At feedback level 1 the second harmonic starts to appear at less than 1/4 the strength of the first harmonic. At feedback level 2, this second harmonic somewhat stronger (at approximately 1/4 strength). At feedback level 3, the first four harmonics are present with the strength of each being about 1/3 the strength of the previous harmonic. At feedback level 4, the harmonic spectrum of the first eight partials of a sawtooth wave become recognizable. We get the first 18 partials at level 5. At level 6 we get what could be called a hyper sawtooth wave, with a very strong peak at partial 34, with lesser peaks running up from partials 26 through 46. Finally, at level 7 we get a white noise spectrum with added strong partials at the first two harmonics.
This analysis bears out when looking at the resulting waveforms in Audacity. We start with a pure sine tone, and with each increase of the level we start to see the sine wave lean to the left a bit. By feedback level 3, a smoothed sawtooth wave is clearly visible. At level 5 we see a pretty close approximation of a sawtooth wave. The waveform at level 6 appears to be 34 periods of sawtooth waves shaped into sawtooth wave type shape at the frequency of the first harmonic. Furthermore, we get a significant amount of positive side DC offset in the waveform, leading to some distortion (we had actually gotten some DC offset at level 5 as well). The waveform at level 7 has a clear profile of white noise, though it seems to have occasional fragments of a noisey square wave. Interesting enough we also get a small amount of negative side DC offset.
Ultimately, what we learn is that feedback shapes an oscillator’s sine wave into a sawtooth wave, peaking at level 5, moving into a hyper sawtooth wave at level 6, and becoming largely white noise at level 7.
Landscapes Update: January 1st, 2020
So I finished the composing for the Landscapes project on December 14th, 2019. Or did I? My wife, who teaches writing, would tell anyone that the key to good writing is revision. Any part that has already been recorded I will consider to be finished, but I plan on making at least one revision every month to one of the Landscapes movements. One of the things I may add is a layer of Musique Concréte to some movements, as it may make the pieces more marketable to festivals and conferences, and it’ll add another layer of timbral interest.
I plan on writing a grant for 2021 that will fund recording efforts for the Landscapes project. Until then I intend on continuing to record parts for the movements on my own. Accordingly, in December I finished a recording of the bass part for Landscape 5: Marsh, which is included below. Today I have made a YouTube playlist of the Landscapes project, so if you wish to hear them continuously, you may. I will continue to post updates on the Landscapes project every month or so, and will update the playlist as I add more recordings. Anyway, as promised, here is a recording of Landscape 5: Marsh featuring Carl Bugbee (from the prominent Rhode Island cover band Take it to the Bridge) on electric guitar, and myself on electric bass.
Low Pass Filter Demonstration
Of the various filters used in subtractive synthesis, the low pass filter is by far the most commonly used. Accordingly it is useful to examine how this filter alters sound. To that end, I’ve made a couple of videos that demonstrate three different filters in Logic Pro’s Retro Synth instrument.
Before getting too deep in the process, I’ll start with some basic information. A low pass filter attenuates frequencies above a set center frequency. Filters are often described in terms of their slope, that is the amount that higher frequencies are attenuated. Slope can be described in terms of decibels per octave. Thus, a 24dB filter dampens frequency content by 24 decibels per octave. To put it another way if the center frequency is set at 100 Hz, audio at 200 Hz should be attenuated by 24 decibels, while audio at 400 Hz should be attenuated by 48 decibels. Thus, the higher the slope, the more effective the filter is at attenuating filtered frequency content. Slope can also be described in terms of poles, which translates out to 6dB. Accordingly, a 24dB filter is also called a 4 pole filter, while a 12dB filter is called a 2 pole filter.
The three filters demonstrated in these videos are a 24dB low pass (described as being Lush), a 12 dB low pass (described as being Creamy for some unknown reason), and a 6dB low pass (described as being Lush). Each is demonstrated with a 4 second, 55 Hz sawtooth wave (A1, where C4 is middle C). In each pass, the center frequency is swept up from the lowest to the highest frequency setting for the filter. Thus, we hear harmonics add in over the course of four seconds.
Additionally, these videos also demonstrate how the filters in question respond to difference resonance settings, which begs the question, what on God’s green earth is resonance? Resonance feeds the audio at the center frequency of the filter back through the filter. At moderate settings this can allow harmonics to be accentuated when the center frequency matches the frequency of a sound’s harmonic. At very high settings quality analog filters self resonate, which means they produce a sine wave at the center frequency even when no sound is patched into the filter. Because resonance creates a peak at the center frequency, it can increase the perceived slope of a filter. Each video features nine passes, three for each filter (24dB, 12dB, and 6dB respectively). The first pass of each group features no resonance, while the second has the resonance set at 50%, and the final has the resonance set at 100%.
What do we learn from these videos? While it would be technically incorrect to say that these filters all self resonate, we can say that they are coded to emulate self resonating filters, so for all intents and purposes, these filters are functionally self resonating. Thus, when the resonance is turned up to 100% we hear a sine tone sweep up the entire frequency range of the filter in addition to the filtered 55Hz sawtooth wave. Furthermore, we can see that sweep in a linear fashion in Logic’s graphic equalizer, confirming it responds in a linear fashion in pitch space, or exponentially in frequency space. The resulting wave form is basically a sine wave laid out over the structural form of a longer period sawtooth waveform. One odd thing we notice is that the 12dB (Creamy) filter peaks severely when the resonance is turned up to 100%. I found this to be true at every key velocity.
We also hear that the filters effectively accentuate harmonics when the resonance is set at 50%. This allows us to hear the exponential curve of the filter. As the center frequency moves up linearly in terms of octave pitch space, it accentuates increasing numbers of harmonics as the more harmonics are grouped within an octave as you sweep up the frequency range.
We can also hear and see how much more effective the higher slope filters are than the lower slope filters. We can see how the higher slope filters effectively squelch higher frequencies when the center frequency is low. Likewise, we can see how much more curved the output waveform is when the center frequency is low.
Here we can see the waveforms as each filter is tested . . .
Here we see the spectral analysis of each tone as evolves in Logic Pro . . .