This section covers how to interactively change tempo using the Beat Counter. Due to conceptional similarities the Tap Tempo will be covered as well which itself is not related to the widget displayed above.
The Tap Tempo allows you to change the tempo at any time - with transport rolling or stopped - within Hydrogen. To change the tempo, hit the \ key in the tempo you want.
After two keystrokes the tempo will be first changed according to the time difference between the two taps. With each addition keystroke the tempo will be changed again to the rolling average of the last up to eight hits of the \ button. If you tap accidentally, or if you wait too long between taps, the Tap Tempo counter will start over.
The widget shown above is the one of the Beat Counter. The Tap Tempo itself does neither have a dedicated widget nor any option to be set by the user.
The Beat Counter is essentially a Tap Tempo on steroids. By default the Beat Counter widget is not visible. To see the Beat Counter widget click the button or simply press ,.
The tempo that you tap will be considered to correspond to even beats of the song's
beat type. The beat type can be set to 1/8 (for eight-note beats), 1/4 (for
quarter-note beats), 1/2 (for half-note beats), and 1/1 (for whole-note
beats). To change the beat type use the left + / - buttons. To change
the Countdown Counter value, use the right + / - buttons. The Countdown
Counter value can be set between 2 and 16 beats. (I.e. if you set the beat to 6, you will
have to tap 6 times before the new tempo is computed and set.) When the
display shows an
R, it means that the Beat Counter
is ready to start from 0. When you tap ,, the
R will change to
1, and will increment with every keystroke until it reaches the Countdown
Counter value (shown just below the
The button in the bottom right-hand controls the auto-start feature, and it toggles between and . When it shows the latter (for Play), the song will set the new tempo and automatically start to play after you tap the right number of beats (if it's not already playing, of course). This way, if you have the Beat Counter set up for 4/4, you can tap 1-2-3-4, and start playing on the next beat. When it shows (for Set BPM), the auto-start is disabled.
For example: Suppose you have a live band, Hydrogen, and a softsynth that is controlled by Seq24)... and you want them all to start at the same time. Set the beat type to 1/4 and the number of beats to 4. Enable auto-start (button shows ). Count off the band 1-2-3-4 (while tapping the , key) and everyone starts on 1.
Another example: Same situation, but the song doesn't require Hydrogen or synths until some point later. During that time, a human (e.g. guitar player) will be setting the tempo. On the measure before Hydrogen is supposed to play, tap the comma key 1-2-3-4 with the beat... and you're in on the next beat (at the right tempo).
An temporal offset when starting the playback after setting the tempo and a latency compensation for the Beat Counter can be configured in the General tab of the Preferences Dialog.
If you are using JACK transport in the presence of an external JACK Timebase Master, Hydrogen is supposed to be a slave and both Tap Tempo and Beat Counter will be disabled. If Hydrogen itself is the JACK Transport Master, tempo changes from Hydrogen will be broadcasted to other JACK clients.