10 Reasons Why High Quality Audio Cassette Tapes Can Sound Muddy or Dull

Bob Leggitt | Friday 28 August 2020
Audio cassettes

In some cases, an audio cassette is expected to sound dull, muddy or woolly. Some tapes were manufactured to a very low budget, with an unsophisticated ferric-oxide formulation. And one of the consequences of skimping in such a manner would be a loss of treble response. But when you’re using a high or metal bias cassette, the expectation is that it’ll reproduce pretty good detail at the top end of the frequency spectrum.

So, you have your chrome tape in the deck, and it’s sounding way more woolly than you expected. Why is that?

Here are ten of the the most common reasons…

The play head is dirty. Dirt or grease on the play head is one of the most common reasons for substandard performance in audio cassettes. Regular cleaning of the heads in your equipment will help keep the definition as bright as possible, and significantly reduce the likelihood of longer-term problems.

The heads or tape are out of alignment. The alignment of the tape across the heads is critical to the reproduction of treble detail. Just a small discrepancy in alignment is enough to mute some of the treble and make the cassette sound dull.

One of the most common instances of this occurs when you have two tape decks with slightly different head alignments. If you record on one deck, and play back on the other, the definition of the playback will be compromised. The build quality of the actual cassette can also cause alignment problems. And old tapes that are starting to seize up a little may experience drag, which can interfere with the alignment of the tape. I’ve had success re-casing old, drag-afflicted tapes. Housing the old reels in a new cassette casing can free up the drag and better align the basic travel. The transformation is sometimes remarkable, with full treble restored.

You’re using Dolby on a tape that was not recorded with noise reduction. The Dolby noise reduction system was designed as a two-step process, in which both the recording and the playback require technical modification. If you have a tape recorded with Dolby, and you play it without Dolby, not only will you hear noise – you’ll often also find the tone is too bright. But if a cassette was recorded without Dolby, and you play it with the Dolby switched in, the opposite happens. It loses its essential top end, and typically sounds woolly or muffled.

The record head was dirty when the recording was made. This is something that can’t always be rectified retrospectively. Typically, the only way to rectify a dull recording that was made with dirty heads is to clean the heads and re-record it. If re-recording is not possible, there’s little you can do.

A stereo recording is set to play in (forced) mono. Some reproduction systems have a button you can press to force a recording to play in mono. The function was really designed for use when there’s only one speaker, and some elements of the stereo image would otherwise be lost. A professional stereo recording is normally fine when played in forced mono, because professionals understand how to control the phasing of the audio signals. But some badly phased stereo recordings will corrupt when set to play in mono, and one of the possible symptoms is a drop in treble – a characteristically dull sound. The quick solution on stereo equipment is to disengage the Mono switch and let the recording play in stereo. On mono equipment, there’s no real way round the problem.

The cassette has a low grade formulation. Not all high bias tapes had naturally zingy sound. Some were barely any brighter than a decent normal position tape. Actual chrome would typically have great definition, but many high bias tapes were not chrome – in some cases, even if the brand on the packaging used the word “Chrome”. High bias, per se, does not signify any qualitative standard of formulation. As long as the bias met the criteria, the formulation could vary very significantly.

I’ve never had a metal tape with an inherently dull sound, but I have had various high bias which, whilst not exactly woolly, have not produced anything like the crispness of chrome.

You’ve been “eBayed”. One of the most fortunate traits of the audio cassette can also prove to be one of the most unfortunate. The facility to take the reels out of a cassette and re-house them can save an old recording suffering from dodgy alignment – as we’ve seen. But that same facilty also means a seller can transfer low quality tape reels into high quality brand casing. If you’re not buying sealed packages, it’s almost impossible to verify that the tape reels in a secondhand cassette are original. It would be extremely na├»ve to imagine that every cassette sold secondhand was precisely as described.

The pressure pad has dropped or dislodged. On the cassette, just behind the tape at the point where it will touch the deck’s heads, there’s a small pressure pad that should keep the tape/head contact firm. Especially on old tapes, this pressure pad can “drop” – meaning the metal spring loses its push and the pad relaxes back a little. The “drop” of the pad can also be uneven, so the contact is, say, still firm in the middle of the tape, but less so at the edge. This can cause all sorts of sonic problems, including muddiness. It’s sometimes possible to reassert the pad so its contact is once again strong (don’t overdo it though, as that will cause problems too). But I will normally move the reels into a completely new casing when the pad drops.

Your hi-fi lost some treble. It sounds terribly condescending, but this has happened to me on more than one occasion, and it’s often the last thing I check. Check your treble control and/or graphic equalizer. But more than that, check the whole front face of your hi-fi if something sounds dull. Different systems have different switches and selections. Make sure everything is set the way you usually set it. Even something like a Loudness switch can result in a treble drop if you normally have it switched in, and it gets switched out. And while you’re about it, put an ear up to the tweeter area on both your speakers. I did that some years ago and found a tweeter had a cracked solder joint, which needed reheating.

The external recording equipment was/is faulty or compromised. External equipment comprises everything outside the tape deck, including the microphone, and the cables, which are a very frequent cause of treble loss in recordings. When you record – particularly with complex setups – it’s best to monitor directly from the cassette deck. That is, take a stereo feed straight out of your deck’s output, and plug it into the monitor. If you monitor from anywhere else, you could be missing problems with treble loss.

If an input lead has a poor contact you may be feeding dull sound into the cassette deck. And unless you’re monitoring post-deck, you won’t know, because the main substance of the audio will still register on the deck’s visual meter. It sounds and looks fine until you play back, and then you hear a muddy tone. Always monitor from the tape deck’s output. Then you can be sure the input is okay.

So there are quite a few ways in which a cassette's audio integrity can be compromised. But keep an eye on the common problems described above, and the chances of that dull, woolly sound plaguing your audio entertainment, will be minimal.