Gamma Knife is written in the key of D Dorian. According to the Theorytab database, it is the most popular key among Dorian keys and the 26th most popular among all keys. The D Dorian scale is similar to the D Minor scale except that its 6th note is a half step higher (B). Chord progressions in Dorian have a characteristic sound due to the major quality of the chord built on the 4th scale degree. See the D Dorian Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!
The original MIDI standard was later augmented to include the Standard MIDI File (SMF) specification, which describes how MIDI data should be stored on a computer. In the following, we denote SMF files simply as MIDI filesor MIDI representations. The SMF file format allows users to exchange MIDI data regardless of the computer operating system and has provided a basis for an efficient internet-wide distribution of music data, including numerous websites devoted to the sale and exchange of music. A MIDI file contains a list of MIDI messages together with timestamps, which are required to determine the timing of the messages. Further information (called meta messages) is relevant to software that processes MIDI files.
Gamma Note MiDi
The most important MIDI messages are the note-on and the note-off commands, which correspond to the start and the end of a note, respectively. Each note-on and note-off message is, among others, equipped with a MIDI note number, a value for the key velocity, a channel specification, as well as a timestamp. The MIDI note number is an integer between $0$ and $127$ and encodes a note's pitch, where MIDI pitches are based on the equal-tempered scale. Similarly to an acoustic piano, where the $88$ keys of the keyboard correspond to the musical pitches A0 to C8, the MIDI note numbers encode, in increasing order, the musical pitches C0 to G$^\sharp$9. For example, the concert pitch A4 has the MIDI note number $69$.
The following figure shows various symbolic music representations of the first twelve notes of Beethoven's Fifth including a sheet music representation, a MIDI representation (in a simplified, tabular form), and a piano-roll representation.
An important feature of the MIDI format is that it can handle musical as well as physical onset times and note durations. Similarly to sheet music representations, MIDI can express timing information in terms of musical entities rather than using absolute time units such as microseconds. To this end, MIDI subdivides a quarter note into basic time units referred to as clock pulses or ticks. The number of pulses per quarter note (PPQN) is to be specified at the beginning, in the so-called header of a MIDI file, and refers to all subsequent MIDI messages. A common value is 120 PPQN, which determines the resolution of the time stamps associated to note events.
Like the sheet music representation, MIDI also allows for encoding and storing absolute timing information, however, at a much finer resolution level and in a more flexible way. To this end, one can include additional tempo messages that specify the number of microseconds per quarter note. From the tempo message, one can compute the absolute duration of a tick. For example, having 600000 $\mu$s per quarter note and 120, each tick corresponds to 5000 $\mu$s. Furthermore, one can derive from the tempo message the number of quarter notes played in a minute, which yields the tempo measured in beats per minute (BPM). For example, the 600000 $\mu$s per quarter note correspond to 100 BPM. While the number of pulses per quarter note is fixed throughout a MIDI file, the absolute tempo information may be changed by inserting a tempo message between any two note-on or other MIDI messages. This makes it possible to account not only for global tempo information but also for local tempo changes such as accelerandi, ritardandi, or fermate.
The file format specifications for MIDI are complex and go beyond the scope of the FMP notebooks. The good news is that there are various software tools for parsing, manipulating, synthesizing, and storing MIDI files. In the following, we introduce the Python package PrettyMIDI for reading MIDI files. Furthermore, this package transforms the (often cryptic) MIDI messages into a list of easy-to-understand note events. The following code cell parses a MIDI file, converts the data into a standard Python list, and displays the first MIDI events in a table. We continue with our Beethoven example from above.
Finally, we plot the MIDI data in a piano roll representation, where the color (given as RGBA value) of each rectangle is determined by a note's instrument (RBG value) and velocity (alpha parameter, opacity). We now use a visualization function from libfmp that has been introduced in the notebook on our CSV format for symbolic music.
We can convert a list of note events into a CSV file with the to_csv method of a pd.DataFrame. In the following code cell, we convert a MIDI file into a CSV file as used in the FMP notebook on the CSV format.
Another package for piano roll visualizations is pypianoroll. The functions to convert a midi file to a list of note events as well as the pianoroll visualization function have been included into libfmp. In the following code cell, we call those libfmp functions:
Potency determination of B. anthracis strain Ames compared to that of the Pasteur strain. Nineteen twofold dilutions of gamma phage preparation were spotted identically on 5% sheep blood agar inoculated with B. anthracis strain Ames (left) versus strain Pasteur (right) and then incubated at 35C for 18 h. Arrows identify a macroplaque and an area containing microplaques used for calculating PFU per milliliter.
It is obvious from these studies that an accurate assessment of phage preparation activity and quality control requires the use of both pXO1-positive and pXO1-negative strains. The negative strains (such as the Pasteur strain) allow accurate plaque counts, whereas the pXO1-positive strains assess the potency of the preparation to identify fully virulent strains such as the Ames strain. The basis of the increased sensitivity of strains lacking the pXO1 plasmid compared to that of positive strains is not understood. As the pXO2 plasmid appears to have no effect on the response to the gamma phage, avirulent strains such as the Sterne strain can be used with the avirulent Pasteur strain to determine potency and to perform quality control assessments. Recent data, not reported here, suggest that the effect of the pXO1 plasmid may be more indirect. It has been our observation and that of others that strains possessing the pXO1 plasmid sporulate more readily than those lacking pXO1. As was seen in this study (data not shown), Gram-stained 18- to 20-h growth from pXO1-positive strain cultures on SBA showed high numbers of spores, whereas those from Pasteur-like strains lacking pXO1 typically showed very little, if any, spores. The net result is that growth material used from primary culture of a pXO1-positive strain to test for gamma phage sensitivity would contain larger amounts of spores, cell wall debris, and dead cells containing endospores than material from a pXO1-negative strain. In theory, when gamma phage is added to the inoculated surface, much of the phage may be binding to receptors in this debris and once bound are incapable of infecting bacilli later emerging from the germinating spores. However, when inoculated onto Pasteur-like strains, there is minimal competing debris, and phage binds to and infects viable bacilli. The net result is that fewer phages are required to generate a plaque. This is supported by our observation that when washed Sterne spores were used as the inoculum rather than growth from primary culture, clearly defined macroplaques were generated at much higher dilutions, similar to those of the Pasteur strain.
To date, gamma phage prepared using the host strain, B. anthracis CDC684, and filter sterilized using low-protein-binding 0.22-μm filters to remove bacteria has shown remarkable stability over 2 years while being refrigerated at 4C. This is contrary to the previous findings of others (6), who found it necessary to frequently prepare fresh batches of gamma phage. The stability of gamma phage preparations produced as described here allows individual gamma phage preparations to be employed for long-term use and dispersal to multiple laboratory locations with minimal loss in activity. At this juncture, several preparations have undergone analysis for potency and pour-plate PFU per milliliter determinations. Phage lot TA101201, prepared in October 2001, showed less than a log10 drop in PFU concentration from 2001 to 2004 and retained its activity towards fully virulent B. anthracis strains when tested for potency. Likewise, other lots such as TA022303 also showed less than a log10 decrease from February 2003 to February 2004, whether measured using the potency or the pour-plate assay. Since there is less than a log10 decrease in potency, it is reasonable to assign a preparation an expiration date of at least a year if it produces distinct macroplaques when diluted 1:8 to 1:10 or more in nutrient broth and applied to the first and second quadrants of a test strain possessing the pXO1 plasmid, such as Sterne. In general, our preparations are sufficiently stable for 18 months to 2 years. According to an unpublished method dated January 1971, originally provided by W. Cherry, Analytical Bacteriology Unit, CDC, acceptable phage preparations can be used either undiluted or diluted 1:10, and phage preparations having concentrations less than 107 PFU/ml should not be used. Our observations were consistent with those statements.
The findings show the reliability of this simple biological assay for identifying B. anthracis. However, we continue to stress that confirmatory tests should be used along with this gamma phage assay for positive identification. Validation studies showed lytic behavior to be as expected for all isolates, giving an assay specificity of at least 98% for B. anthracis. Gamma phage application in the two quadrants was an essential element of robustness and tolerated variation in inoculum load. Finally, B. anthracis strain CDC684 appears to be an excellent host strain for production of batches of high-titer, stable gamma phage when produced in the manner described here. 2ff7e9595c
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