M² Performance Reports
In the quest to hold repair shops to a higher standard, at the end of 2021 M2 Circuits introduced a standard performance report. The performance report contains all of the relevant specifications of your equipment like reference output levels, distortion, noise and more. Every repair and alignment comes standard with a report. This ensures that the unit is thoroughly tested before being marked complete.
With the majority of hifi and studio equipment the following parameters are tested:
- Total Harmonic Distortion
- Signal to Noise Ratio
- Frequency Response
When it comes to reel to reels and cassette decks there a few more pieces of information required for an accurate depiction of a unit’s performance. These include:
- Reference Fluxivity
- Record Wow and Flutter
- Play Frequency Response
- Record Frequency Response
- Record Bias Settings
- Optimal Record Speed
The frequency response graphs that come with the standard report are plotted by hand using spot frequencies. For all units, except 2-head cassette decks, an audio analyzer plot can be provided upon request. Tests are completed using a Ferrograph RTS2 Recorder Test Set and a Quantasylum QA401 Audio Analyzer.
Here are a few notes to clarify some of the specs on the performance report.
Record Wow & Flutter (W&F)
The W&F figure given in most, if not all service manuals and brochures is for playback only. When recording a tape the W&F figure is normally twice as high than the given figure by the manufacturer.
Therefore, we give the the Peak Record W&F. This is a more accurate number than just playback, as most people use their tape recorders to record tapes! W&F is measured by sending a 3kHz sine wave to a tape deck, recording it, and playing it back to see how much the frequency varies. A Ferrograph RTS2 Recorder Test Set is used to measure the peak W&F.
Play Frequency Response
The play frequency response of a tape recorder has to be plotted by hand, as we use the response section of the test tape to measure it. Unfortunately, test tapes only give spot tones at specific frequencies. This gives the graphs a “blocky” look since there are no data points available between the tones.
One thing to note, is the bass response on the playback graphs. Full track test tapes suffer from something known as fringing, which makes the bass response look bloated – often giving values of +4dB above the reference level at frequencies below 100Hz. This is why in all service manuals it is recommended to make low frequency playback adjustments while in record mode. A quote from the MRL test tape document on fringing, “When the recorded track is wider than the reproducing head core, the reproducer will show the low-frequency boost mentioned above due to fringing.”(Choosing and Using MRL Calibration Tapes)