Monthly Archives: January 2019

How to clean up Portastudio tracks

I am using Reaper Digital Audio Workstation (DAW) to clean up old Portastudio tapes that I copied to my PC. (See previous post). Reaper is inexpensive and you can use it for free to try it out. It is a very sophisticated program that runs on a Windows PC and is of audio studio quality.

So, first step: Fire up Reaper, start a new project and copy the 4 track Portastudio WAV files into the workspace. Simply drag and drop the files and get Reaper to arrange them as 4 separate tracks..

 

The next screenshot shows the 4 tracks with a whole cassette of music. We are working on a single song, so select all the tracks and set a selection around the part we want. Right click and select “Crop project to selection”.

 

 

You will then get just the required bit of music to work on. Note that there is no danger of deleting or altering the original WAV files. In the cropped view you can see that track 2 contains a drum machine track. This is to be replaced by a MIDI drum track.

At the moment I have no idea of the tempo. It is in 4/4 time. So I select all tracks and play from the start.

I press the SHIFT W key at the start of every bar and try and get these as accurately placed as possible. This creates a special time stretch marker (shown as a vertical line on the trace) that can be moved to stretch/reduce the time base for the music. If I move the marker to the left it will speed up the music on the left up to the next marker and slow up the music on the right up to the next marker. The neat thing about this is that the start of the bar can be adjusted to line up exactly with a fixed tempo grid.

 

The above screenshot shows all the markers added. You can see that the underlying grid is set to 120 bpm (beats per minute) tempo and does not align with the added markers. The next step is to calculate the average tempo and set the tempo grid so that the markers will line up.

 

The above screenshot shows just the drum track with markers. Position the cursor on the first marker and read off the time display. You then position the cursor on (say) the eleventh marker and read off the time display. You can then work out the time interval for 10 bars of music and hence calculate the bpm.

In my example:

cursor @ 1 time = 4.8 S

cursor @ 11 time = 37.7 S

Time interval = 37.7 – 4.8 = 32.9 S

Number of bars = 10

Number of beats in 4/4 = 4 * 10 = 40 beats

Tempo (bpm) = (40 x 60) / 32.9 = 72.9 bpm

 

The next step is to adjust the underlying grid so that the markers align. There is a field to enter the tempo (bpm) under the displayed tracks. When this is changed, Reaper will by default time stretch or reduce the tracks in order to change the tempo. At the moment we do NOT want this behaviour, but adjust the tempo grid independently of the music tracks.

The way to do this is to temporarily turn off the time stretch/reduce function. Go to the “File” main menu and select “Project Settings”. Set the two “Timebase” values to “Time” as shown below.

Enable the editing function “Item Edit Grouping Enabled” to allow all tracks to be edited in one go and also turn “Snap To Grid” to off.

Enter the calculate tempo (72.9) to the “bpm” field and this will change the grid spacing.

Select all the tracks and move the tracks to align the first marker with a bar start line.

 

If you calculations are right and the original keyboard tapping is accurate, you will see the music line up with the tempo display. In my example above, you can see some slight discrepancies with the markers and the beat lines. In my example it is pretty obvious where the markers should be on the drum machine track.

The next step is to adjust the markers to align with the beat lines on the tempo grid. When these markers are moved, the tracks are time stretched to fit.

Select all the tracks, hover the over the diamond symbol on the marker. The cursor will then change to a diamond shape. Press the left mouse button to grab the marker and whilst holding the mouse button down, move the marker to align to its nearest beat line, then release.

Note that it is possible to select a single track and adjust it independently to correct for timing errors in the original performance and so tighten up sloppy playing. Obviously in my example this is not necessary !

Once the process is complete, go back to the project settings dialog and change the timebase values back to their original defaults (beats). The music can then be changed to any desired tempo and the audio will be automatically time stretched or reduced.

 

In my example I can set the tempo to 85 bpm to speed it up slightly. I can then generate a drum track using a MIDI editor for a tempo of 85 bpm and import it, or I could record a drum machine running at 85 bpm. The old drum track can then be replaced.

 

You can see that the original drum track is muted and a new MIDI drum track has been added as Track 5. I have assigned a VSTi instrument to the MIDI track using the fX button and am using a sound font with a standard drum kit.

Remember the Portastudio ?

I bought a Portastudio 4 track tape recorder in the early eighties. This allowed me to record 4 tracks of audio on a compact cassette tape. The tape spooled at twice the normal speed to increase fidelity. It also had a 4 track mixer and basic studio facilities. The main drawback with this system was that it only allowed a maximum of two tracks to be recorded at any one time. It allowed 4 tracks to be mixed into a stereo output but it had no facilities to output 4 separate tracks at once.

TEAC Portastudio 144

At the time it was the bee’s knees and was very popular with bedroom musicians. I used it in conjunction with a Polysynth that I built and a very basic drum machine. The vocals were questionable !

Wind on thirty years….. I wanted to preserve all my earlier creations and I wanted to get them digitised as the tape deteriorates and the machine will stop working soon. There have been so many advances in digital audio engineering and I have the facilities to edit, improve, add effects etc.etc.

My first attempt was to output two channels (1 & 2) and record them to my PC using a stereo ADC interface, and then record the other two channels (3 & 4). This required two passes of the tape and when I tried to match up the two recordings there were quite serious synchronisation problems.

I then decided to hack the machine and get access to the 4 channels at the mixer. I bought a 4 channel ADC USB interface and hooked this up to my PC.

 

 

I used a superb, cheap DAW (digital audio workstation) application called “Reaper” on my PC and this allowed me to record 4 channels at once. Each track can then be saved as a WAV file.

The Portastudio hack involved the following:-

  1. Take a stereo phono lead and cut in half so that you have 4 phone connectors.
  2. Take the back off the portastudio.
  3. Solder the signal wires to test point connectors on the Mixer part of the exposed PCB.
  4. Attach the screen wires to the chassis.
  5. Plug the phonos into the MAYA 44 USB analog inputs.

Notice the connector labelled “T.P. (TRK 2)” in the centre. Connect a signal lead to it. (actually shown as white). The phone cable screen is connected to the blue/white stripey wire.

 

 

Continue with Tracks 1 to 4.

 

The screen wires (connected to blue/white stripey wire) are connected to the chassis.

 

The Portastudio back is stuck back temporarily and there are 4 phono leads available.

 

I have managed to transcribe all my old Portastudio tapes to individual WAV files. I have managed to do various tasks, for example I have taken off the old drum machine track and replaced it with a more realistic track, I have managed to add extra tracks of instruments, Vocal tracks. I have also managed to edit the tape to duplicate choruses, take out bum notes – that sort of thing.

In order to add extra drum tracks or MIDI sequences it helps to make sure that the tracks are all synchronised to a standard beats-per-minute. I play the tracks together using Reaper and press a key to generate a marker on every bar start. I can then get the average BPM and set up a grid with this figure. I then manually adjust each marker to the grid using the time expand  /compress feature to get the start of each bar to line up with the grid. The adjustments required are very small (if required at all) and do not affect the fidelity. If a track includes a drum machine it is easy to check that the manually generated marker is actually the start of the bar.

Once this has been done, it is easy to run a drum machine along side or add a MIDI track.

I used to bounce 3 tracks into one track in order to free up more recording tracks, unfortunately this cannot be undone and the tracks need to be transcribed by ear and re-played on a MIDI instrument.

I shall show a tutorial for processing the tracks on a later blog entry.