The newest version 1.2.1 is a big update for the HotPaw Music Spectrograph app. It includes a lot of internal improvements in the quality of musical sound analysis, several bug fixes, plus one added major new feature.
My first problem was in deciding whether to keep the word "Spectrograph" in the name of the app. When I looked at journal articles and books published by music professors, I saw at least 3 different terms used to describe these colored 2-dimensional time vs. audio frequency charts: Spectrograms, Spectrographs and Sonograms. These terms also seem to have multiple uses, with Spectrograph also referring to optical devices used to split light into its constituant spectral colors, Spectrogram referring to the picture of a spectrum, and Sonogram referring to the results of ultrasound medical 3D imaging. The term Sonogram, regarding music, is more rare; but I found this term used in a recently published textbook on sound by a professor of physics at Harvard University, as well as in a few other academic works.
In optics, the term "Spectrograph" is used for devices that produce spectrums or spectrograms. Since the HotPaw Music Spectrograph app on an iOS device can be used on real-time sound input and works like a continuous chart recorder, I think a word ending with "-graph" more implies this continuous graphing activity; whereas the "-gram" suffix seems to just imply more a static image. So I'll stick with calling it a spectrograph for now.
Some of the changes in the Music Spectrograph update include 12th-octave frequency band filters which are now better calibrated for the evenness of their response. A few bugs in selecting, converting and playing Songs from your iTunes library to see their spectrograph have been fixed. You can hit the Song button to use, and to turn-off this feature.
Now, there are several apps in the App store that can be used to help transcribe or learn music by slowing down songs without changing the pitch.
Music Spectrograph won't slow music down. The new "ReSynth" feature in Music Spectrograph can actually stop music in time.
The major new feature added to the Music Spectrograph app is sound re-synthesis. Hit the button to "Stop" recording or music playing. Then touch the spectrograph and scroll back to some sound earlier in time. A new button will appear near the top left of the chart. The "ReSynth" button. Scroll to an short sound, such as an eighth-note, and just stop and listen to just that one note or chord in time (but with most overtones and harmony included as well). Scroll back-and-forth to listen to the notes immediately after or before. See how what you hear corresponds to the piano keys nearest the highlighted frequencies. The MIDI note numbers will also be displayed at the top.
What you will hear when using this re-synthesis will just be the strongest portions of the audio frequency spectrum, and those which directly correspond to the pitch of MIDI or piano key notes. This re-systhesis isn't completely accurate, as any transients (such as consonants or percussion) and smaller and non-musical frequencies will have been removed, leaving a sound more like that produced by a vocoder (which is what is happening behind the scenes). If you scroll back-and-forth in time, you might hear some tweeting/chirping noises as various high frequency overtones become large enough to show up on the graph for just a short time.
To use the Music Spectrograph app for music transcription, you will still need to know how to understand and ignore all the harmonics and sequences of overtones in the graph yourself. This is not always easy, as many music instruments and types of human voice produce far more overtones then any sound at the actual musical pitch frequency. This app may be helpful in learning about this important feature of many interesting musical sounds.