Is there any practical difference between 4/4 and 8/8? regards a common and unusual time signature; both 3/4 and 3/8 time are pretty common.
What difference in performance is implied in the the difference between 3/4 and 3/8 time signatures?
What would lead a composer to notate a work in one or the other?
These two time signatures both indicate simple triple time (also known as waltz time). They are mainly used in the same genres:
All of these genres commonly use simple triple time i.e they have three beat per measure (usually with the first beat being the strongest). The obvious differences between 3/4 and 3/8 are the number and length of the beats (there is one other simple triple meter, 3/2). 3/8 has three quavers and 3/4 has three crotchets. However, 3/8 time usually suggests a higher tempo or a shorter hypermeter than 3/4. This is not always the case as there is no strict rule, but it is often implied.
There's no absolute rules as to when a composer should use one over the other - it often comes down to the tempo and feel of the music, but it is subjective. I've (for better or worse) seen Presto 3/4 pieces that go much faster than some 3/8 pieces.
The big difference in terms of timing is that 3/8 is mainly used as a compound time, whereas 3/4 is most commonly conducted in simple time. So if the composer "felt" that a bar should be conducted as a single unit rather than 3 individual beats, that might be a particular reason to choose one over the other. Tempo of course does come into it as well.
Of course, then we get to the question of why 3/8 should be used over 6/8, and so on - sometimes when the phrases work in odd numbers this is clearer, but more often than not it's just at the composer's discretion to emphasise various beats and timings slightly differently.
In the context of Baroque dance music or suites, then there are good reasons to use 3/8 in preference of 3/4 (or vice versa). In the days before metronomes, how the music was notated would be an indication of performance speed. The notation would also be specific to a particular dance.
I have borrowed diagrams from Jan van Biezen, who has written extensively on such subjects:
The above image (figure 1) is fairly self-explanatory (the metronome marks are a modern interpretation of a 1705 French work by l'Affillard, I believe): faster dances with quicker steps are notated in 3/8, slower ones in 3/2 or 3. N.b. it appears that 3 can mean duple 3-time similar to 3/2 as well as what we would recognise as modern 3/4 time.
Now, the following diagram (figure 2) summarises the transitions between using different metres and tempi. Van Biezen writes in Dutch; Geheel means whole as in normal time where you are really concentrating on counting in 3, think of a Menuet (3/4), and Half means half as in half-time, like a Sarabande with a drawn-out beat but with possible subdivision of that beat (3/2).
Figure 2 is saying the following: if your dance/music has a 'whole beat' feel to it, then use one of the time signatures on the left. If it is fast, use 3/8, if it is slower, use 3/4. If your dance has a 'duple subdivision' feel, use a time signature on the right. If it is fast, use 3, if it is slow, use 3/2.
However as time progressed, it seems the antiquated 3 was replaced by 3/4, which is a sort of one-size-fits-all time signature in that it can accommodate both 'whole' and 'half' time feel.
Take four cases (I'm using Bach cello suites as examples because they are based on dances as was the done thing back then, and also because they're awesome pieces of music).
Later on his page, van Biezen also refers to the time signature as determining the shortest value at which notes inégales can be used. It's not strictly important here but is quite interesting, so read the pages linked in this and above paragraphs.
Furthermore, as has been alluded to in other answers, in both Baroque dance music and more modern pieces, 3/8 can be used as the sub-unit of a hypermetre (i.e. counting one-in-a-bar to express a phrase lasting longer than 3 quaver beats). This may be useful if the composer wishes to highlight a sense of urgency in the music, or perhaps if it becomes somehow easier to represent complex cross- and counter-rhythms.
This might be interesting reading too, a discussion on whether Bach really did use time signatures as tempo directions.
Tl;dr: If you're in 18th century Europe and need your crew to know how fast and in what mood to play your new triple-time dance piece, you would choose 3/8 or 3/2 etc. as a matter of convention.
If you're in 21st century anywhere, use the time signature that you think conveys the mood of your piece or which you feel best expresses your phrasing.
3/8 is more suggestive of a single beat per measure (a dotted-quarter note made up of 3 sub-beats) whereas 3/4 is more suggesting of three beats per measure (each a quarter note).
Typically from what I've seen, 3/4 music is conducted using three baton movements per measure, whereas 3/8 music is conducted with a single baton downbeat per measure; I'd consider 3/8 to be closer to 6/8 than to 3/4 in terms of feel and conducting.
While many things said in these answers are correct, I think the actual difference has been missed.
The most important thing to remember when considering the difference between the two is probably that people often speak of 3/8 as having 'three beats in a bar' - but it actually has one.
3/8 has one beat in a bar, 6/8 has two, 9/8 has three, and 12/8 has four, where each beat is a dotted crochet.
There is indeed a difference in the notation of the two, but the main difference is how they feel when you subdivide them (divide them into shorter note lengths such as when counting in your head).
Subdivision is very important for orchestral musicians as it allows them to keep in time and understand how to play rhythms which look strange at first sight when sight reading, for example. Conductors will often tell you about their 'internal metronome' - many constantly hear the subdivision of the beat in their heads while conducting.
So what's the difference?
In 3/8 time, there is one beat in each bar (one dotted crochet) and each beat feels like it's in three - you can split each beat up into three quavers.
In 3/4 time, there are three beats in each bar, and each beat feels like it's in two - you can split each beat up into two quavers.
So, when you listen to a piece in 3/8, you can clap to the beat and, depending on the speed, you can count 'one, two, three, one two three...'.
But when you listen to a piece in 3/4, you can clap to the beat and, as you clap, say 'one two, two two, three two, one two, two two....'
So in conclusion, a 3/8 piece will sound like it's in three, but a 3/4 piece will sound like it's in two, even though there are three beats in a bar.
So whereas it can be very difficult (or not really possible) to tell the difference between 4/4 and 2/4 when listening to a piece, and both are often considered correct in aural exams when it is hard to tell, there is a very notable difference between 3/4 and 3/8, and the two do not actually sound the same.
Hope this helps!
My answer is that it has to do with feel. I heard a concert where the conductor changed from 4/4 to 3/8 quietly he counted "one and two" that implies 3/8 eighths while a 3/4 has : one and two and three and, from this you feel the difference, and the difference is quite big.
For me it depends on context. I'm writing a piece that contains 3/8 and 4/8. Why? Because it begins in 5/8. Obviously 5/8 doesn't translate into a /4 time signature and this way it's easier for the players as they continue to count in quavers instead of trying to switch between /4 and /8 time.
On the other hand, if I was switching between /4 times and I wanted a measure with three beats then I'd use 3/4.
It's also a question of what makes sense. If your piece is more easily notated in semiquavers/quavers, use 3/8. If it's a quaver/crotchet, use 3/4. If it's crotchet/minim, use 3/2. If the time signature divides the piece in a way that's easy to read then you've found the right one.
Both 3/4 and 3/8 have been used over the years for everything from a funeral procession to a one-in-a-bar fast waltz. And 3/8 by no means always implied a faster tempo. 3/8 is unusual in today's popular music, but common in more academic styles.
The 4/4 and 8/8 answer is different. 8/8 is mainly used when the eighth-note grouping is irregular, or even varies from bar to bar.
3/8 and 3/4 traditionally referred to certain type of dances in the old days. as far as the performance is concerned, dances that associate with 3/8 time signature start the phrase in the last beat of the meter, whereas dances in 3/4 start at the first beat of the measure. As mentioned by someone above, 3/8 dance is typically passipied; 3/4 waltz. However, it doesn't really matter now.
someone mentioned that 3/8 gets just one beat and treated as if a dotted quarter note. This isn't typically true unless the tempo marks dotted quarter=mm. However, it wouldn't be uncommon for the conductor to conduct the first downbeat for triple meter piece because they are typically very fast. beethoven 5th symphony 3rd movement for example.
Quite some difference looking into economy. Notice that with quarters you have more divisions you can use before considering them ornamental. With 3/8 such writing may look cluttered since you would have to start counting the number of bars in order to understand the duration. With this goes phrasing and tempo division too. A music sentence is consisting of a specific number of bars, normally 4, and this definitely decides a lot which way it would all be written. Notice that 3/8 has a beam over the notes out of the box, which visually means that the main beat is more diluted.
If you look into the music written in 3/8, it is virtually impossible to rewrite it in 3/4 without at least some potential misunderstandings. The same the other way around. Note that if a note is not connected with other notes this is understood as expressing something on its own, within that frame, while notes connected with beam are suggesting phrasing within the same beat. This is why you regularly have legato over 3/8, which you cannot easily express with 3/4 because it would easily mean something else depending on the instrument.
In that sense, mathematically speaking, you would say that 3/8 and 3/4 are almost the same thing. Musically, they are so different that the choice is predetermined within your initial motive. You simply know with all the rules and intention taking into account (and economy of writing and understanding) instantly which tempo that piece is going to be.
Can you interchange 3/8 and 3/4 and simply, for example, later decide that 3/8 should better be 3/4 or vice versa? No! It is so essential and clear from your intention that one piece may inheritably have only one most precise meter attached to it. The question would be similar for an architecture if you can create the same house using wood instead of concrete. It is possible, of course, but ultimately only one of them is initial and right choice.
In that sense the music architectural context of 3/8 and 3/4 are very different and not interchangeable in any practical sense.
(The question is at the same level of, for example, using beams over the notes. Technically, with a beam or without a beam, notes have the same duration, right? But, connected or not connected notes mean virtually opposite thing regarding phrasing and tempo and beat etc.)
Musical notation is not in any way that precise. This is why it is essential to use anything available to communicate properly the idea and intention. Tempo is so essential that you simply instantly know which one is going to be easier to understand and write. Professionally written music all have the same economy in them.
