Online lessons (and remote communications in general) provide a level of convenience that cannot be matched by in-person lessons, especially for those who may have scheduling, transportation, mobility, or underlying health issues. However, online lessons do suffer from on major pitfall: delay.
Delay, in the context of online communications, is the time difference that a listener will see/hear any type of stimulus from the speaker, and vice versa. It can vary from person to person, and from day to day. Delay can also manifest itself in different ways:
Delay in audio signals, such as speech or instrument sounds
Delay in video signals, such as camera feeds
Desynchronization of audio and video signals, where you can hear sounds before/after the intended action in video
Pay close attention to any remote/online interviews (such as news or sports panel interviews) on TV, the radio, or YouTube, and you will notice that even professionals will experience delay.
Although delay tends to manifest itself as audio or video problems, the root cause of delay can vary.
The primary cause of delay is your overall internet speed. Slower internet plans will result in slower data transfer from you to your lesson participant. Normally, this delay can only be in milliseconds (between 50-100ms with average internet plans), but remember that your participant's internet speed will also add to this delay. Therefore, to have the closest experience to in-person communication, you and your lesson participant should aim for the fastest internet plan that both of you are willing to afford.
Aside from internet speeds, delay can also be caused by various parts of your setup. This delay can be very small, but can add up depending on your setup and can include:
Overall device speed (its ability to process data into audio and video signals)
Monitor/screen response times (LCD monitors have an average response time between 5-10ms)
Wired Ethernet connections (100 Mbps to Gigabit connection speeds)
USB connections for devices (USB 3.0/3.1 devices being faster than USB 2.0)
Once again, this applies to your lesson participant as well, so their setup related delay will add on to the existing delay from your own setup and internet plan.
Wireless connections of any kind usually cause more noticeable delay. If you are able to use a wired Ethernet connection instead of WiFi, it is highly recommended you to do so (see Using a Wired Connection). Bluetooth speakers and headsets are also huge offenders, regardless of brand or quality. Bluetooth audio devices can also be prone to unusual sound warping or pitch shifting that occurs when the device's pairing signal degrades or experiences a sudden delay.
You can still have a very positive experience with online lessons regardless of delay issues. In fact, effective online learning has become a reality over the last 5-10 years with huge strides in internet communications and information technology. In order to increase the effectiveness of online lessons, teachers (and to an extent, students) should make some adjustments to communication methods and lesson content to minimize the effect of audio/video delay.
As mentioned in Proper Online Lesson Etiquette, teachers and students should take turns communicating instructions, questions, and concerns. Actively trying to interrupt the speaker, combined with varying levels of audio delay, can cause a lot of confusion which ultimately cuts into lesson time. Instead, treat verbal communication like an interview, asking clear and concise questions and allowing the other participant ample time to answer uninterrupted.
The above also applies to demonstrations and performances on your instrument. Teachers should allow students to perform their pieces as uninterrupted as possible, then discuss adjustments or demonstrate corrections when the student has either completed the section/piece or hit a roadblock. This may be difficult for teachers who employ a very active teaching style that reacts to every mistake, but once again, interruptions compounded with delay can cause a lot of confusion for both you and your students.
Students should allow their teachers to also perform or demonstrate uninterrupted. Again, due to delay and the speed of which some pieces are played, an innocent statement like "that part!" can confuse the teacher as to which part the student is referring to.
Practicing or performing exercises and pieces from books are normally not affected by delay directly. As described above, its the communication that occurs before or after a performance or demonstration that commonly falls victim to delay-related issues. Therefore, when you want to focus on a certain part of a piece or exercise, use page and/or measure numbers to verbally target the point of interest. For example:
Student: "I keep getting stuck on bar/measure 21."
Teacher: "On the 3rd page, don't forget the staccatos from measures 46-49."
Some ear-training and rhythm exercises be confusing when audio delay is present. For example, it is practically impossible for the teacher to count aloud or use a metronome for the student while playing during online lessons. Instead, allow the student to count aloud or use a metronome on their end, which will provide real-time rhythm management for the student. Clap-along exercises also suffer from audio delay, so instead of clapping at the same time with the student/teacher, use clap-back exercises similar to those used for Royal Conservatory of Music exams.
For teachers that like to do play-along accompaniments and duets, delay can also cripple traditional methods of accomplishing successful duets and jam sessions. This doesn't mean that you have to take this aspect of lessons out of your curriculum, you just have to find methods to emulate the in-person experience of playing along with students. You can record accompaniments prior to lessons and send them to students so that they can play along with the recording. When dealing with lead sheets, YouTube offers many prearranged backing tracks that your students can search and play along to. You can also arrange chord pattern loops (through recording or apps) to practice performance aspects, like trading solos in improvisational music, although both teacher and student will have to take turns by playing/pausing the recording. It is not perfect, and will never replace the in-studio experience of communicating through music in real time, but with the right approach, the teacher and student can make it work.