Free Slow-Down Tool for Transcribing Bass Lines

Load a recording from your phone or computer, loop the phrase you’re working on, and slow it down without changing the pitch. You can also shift it up an octave, boost the low end and save every phrase you loop. It’s free, there’s no signup, and nothing gets uploaded: the file plays right in your browser and never leaves your device.

Under the tool is how Cole Davis transcribes by ear, step by step, and which part of the tool helps at each step.

How to use the slow-down tool

1. Load a track. Choose a file, or drop one on the tool. MP3, M4A and WAV are the safest bets. No file handy? Press Try the demo line.
2. Loop a phrase. Drag across the waveform, or press Set A and Set B while it plays. Drag the A and B flags to fine-tune the loop, or use the minus and plus buttons, which move them 0.05 seconds at a time.
3. Slow it down. Pick 50% or 75%, or use the slider to go anywhere from 25% to 100%. The pitch doesn’t change. Tick “Speed up 5% each time the loop repeats” and the loop climbs back toward full speed while you play along.
4. Shift the pitch if you want to. Octave up moves a low line up an octave without changing the speed. You can also move it a semitone at a time, as far as an octave up or down.
5. Bring the bass forward. Bass boost turns up everything below about 250 Hz. Cut the highs takes the top off the mix. If the bass is panned to one side, Left or Right puts it in both ears.
6. Save your phrases. Every loop you save gets a number. Tap it, or press 1 to 9, to jump back to that phrase. The tool remembers your loops for each file in this browser, so they’re waiting when you load the same file tomorrow.

On a computer, Space plays and pauses, A and B set the loop, L turns the loop on and off, and the minus and equals keys go 5% slower or faster. The full list is under Keyboard shortcuts in the tool.

How to transcribe a bass line with it

Cole transcribes in the same order every time. He walks through it in how to transcribe bass by ear, where he learns Jaco Pastorius’s solo on “Havona” in real time. Here’s that process, with the part of the tool that fits each step.

1. Get it in your ear until you can sing it

Cole’s process is “getting it in my ear first to the point that I can sing it and then translating it on the instrument.” You don’t have to be a singer: “I’m not a singer … I’m approximating it with my voice.” He does this on everything he learns: “I transcribe with my voice first and I use my instrument to reflect what I’m hearing.”

In the tool: loop the phrase and set Pause after each loop to 2 or 4 seconds. The gap is your turn to sing it back before it comes around again.

2. Find it on the bass, one phrase at a time

Play what you think you heard, then check it. On “Havona,” Cole keeps asking, “Is that actually what it is?” When he doesn’t think he’s got it: “Let me hear it again. I gotta hear it again.” His test: “A good way to check is if what you’re singing lines up with the phrase. That’s how you know.”

In the tool: that’s the A-B loop. Loop one phrase, hear it as many times as you need, and save it before you move on to the next one. If the line is buried, try Bass boost, Cut the highs or Octave up.

3. Check the rhythm, not just the notes

“You can have the notes right and you can have the rhythm wrong.” Where does the phrase start and end? Don’t assume it’s on the one.

In the tool: drop the loop to 50% and listen for exactly where the phrase starts and ends against the beat.

4. Play it without the track, then get it up to speed

Once you’ve got a section, play it without the record. Cole calls that “really important because you want to make sure that you can play it as if it’s your own solo.” When he tried “Havona” along with the track, he didn’t have it yet, so he moved on, “because it’s actually good to get the whole solo and then try to get it up to speed.”

In the tool: start the loop at a speed you can play, tick “Speed up 5% each time the loop repeats,” and let it climb back to 100%.

If it takes you longer than it takes him: “It doesn’t matter. You can still do this. It might take you two or three days.”

Don’t slow down what you already know

Slowing a track down isn’t always the answer. When Cole went to line “Havona” up with the record, he chose not to: “I’m actually not gonna slow this down because it’s a solo that I know already, in that I’ve heard it so many times, so slowing it down only works to my detriment. If I slow it down, I’m handicapping myself … All I have to do is get my muscle memory up to speed.”

So use the slow speeds to find notes and rhythms you can’t hear yet. Once you know a phrase, take it back to 100%.

Then make it yours. “I take it from the solo and then I improvise on it myself. That’s how we integrate these solos into our own language.”

If singing it first is the step you skip, that’s the one to work on. Sing it, find it on the piano, play it on your instrument: that’s the method Cole teaches in Play What You Hear.

FAQ

Does the tool upload my file?

No. The file plays from your own device, right in the browser, and nothing is sent anywhere. The page saves your loop points, speed and saved phrases for each file in this browser’s storage, so they’re back the next time you load the same file. Clearing your browser data clears them.

What audio files can I use?

Anything your browser can play. MP3, M4A and WAV play in every major browser, so they’re the safest bets. Other formats depend on the browser, and if yours can’t open a file, the tool tells you. It needs an actual file on your device, so it can’t open a song inside a streaming app.

Does slowing it down change the pitch?

Not in a current browser. The tool asks the browser to keep the pitch when it changes speed, and recent versions of Chrome, Edge, Firefox and Safari all do. If yours can’t, the tool tells you under the speed slider.

How do I hear the bass better?

Try Bass boost first, then Cut the highs to take the top off the mix. If the bass is panned to one side, Left or Right puts it in both ears. Octave up moves the whole recording up an octave at the same speed.

Should I slow down a solo I already know?

Cole doesn’t. On “Havona,” a solo he’d heard “so many times,” he said “slowing it down only works to my detriment. If I slow it down, I’m handicapping myself.” Slow down to find what you can’t hear yet, then practice at full speed.

Keep going

• How to Transcribe Bass by Ear: My Real-Time Process on Jaco’s Havona
• How to Learn Jazz Standards on Bass (and Walk Them Without a Chart)
• Jaco Pastorius Bass Lines: Teen Town, Havona and How to Learn Them
• How to Play Along With Jazz Records: Lock In With the Bass Player
• Free Walking Bass Line Builder

Sources

• Cole’s quotes on transcribing: How to Transcribe Bass by Ear, from his lesson Transcribing Havona in Real Time.
• “I transcribe with my voice first”: Cole’s video The Fastest Way to Learn Any Jazz Standard, written up in How to Learn Jazz Standards on Bass. The Play What You Hear method is from the course page.
• Which browsers keep the pitch when they change speed: MDN Web Docs, HTMLMediaElement.preservesPitch, and the browser compatibility data behind it.
• Which file types every major browser plays: MDN Web Docs, Web audio codec guide (MP3, and AAC in MP4/M4A), and Can I use: WAV.