Monday January 2, 2023; 6:10 PM EST
- (11 min read)#
- #
- A cassette recording is not a copy. You can make an exact copy of a digital file, and each time you load that file you will get the exact same series of bytes. A cassette recording is literally a recording of a specific event. It is a record of reality, as it exists at that moment. It's the intersection of the audio signal, measured by a specific source device such as a Super Audio CD player, and captured by imposing magnetic flux onto a particular tape by a particular cassette deck. The recording is a captured performance of specific set of conditions, each of which contributes to the final sound. #
- Every cassette recording is literally unique in the universe. The cassette deck is a physical device, and mechanical devices are not perfect. Tape heads, capstans and pinch rollers get dirty. The motors spin as consistently as possible, but there is always wow and flutter. As a painter may work on a stretched canvas, or paper, or cardboard, the tape itself is also a physical medium. Each has its own characteristics, such as how much signal it can take, how much noise the tape itself provides, how much bias it takes to properly orient the tiny magnetic particles.#
- The final sound, at playback, is another performance, created in real time by a physical device, a cassette deck which measures the magnetic flux on the tape. This signal is amplified, and used to drive a preamplifier, amplifier, and then speakers or headphones. Every time you listen to a cassette, it is a specific, particular, unique, individual experience. A performance, a rendition of a specific reality, created in real time. #
- This weekend I have been making recordings from my NAD 6300 Monitor Series Cassette Deck. I spent the past several weeks aligning this deck. Most of the adjustments you make are related to recording, and the pots and variable capacitors are extremely sensitive to the smallest movements. Sometimes you're just applying pressure, rather than turning. And once you've made that feather touch, you record a test signal for ten seconds, adjust the test signal to a higher frequency, record another ten seconds. Then you rewind the tape, and play it back. #
- Measurements are taken from test points at the input to the Dolby circuitry, at the minimum levels you can record. Input around 6 mV results in a measurement of around 40 mV. You watch values change on the multimeter, which you have set to maximum digits, and adjust the meter's rate so it gets a steady value on the first frequency, and set that as your zero dB reference. Then you watch for the change in voltage at the higher frequency. You want the difference to be as small as possible. To be in spec, it should be within 0.5 dB. If it is not, make the adjustment again, and redo the recording.#
- Each individual nudge-record-adjust-frequency-measure cycle takes a minute or so. There are more than two dozen variable resistors and tuning filters to be adjusted, and it can easily take a dozen or more attempts before you get one into spec. These are resonant circuits, which means they have a specific point at which they are in tune, and you can't just turn a pot until it reaches maximum. Maximum will be somewhere in between the extremes, and that point will shift as you tune the other parts of the circuit. Some of the steps affect adjustments made in previous steps, so you go back and fine-tune those, another half-dozen more adjustments to something you've already tuned.#
- If you are patient, you can get all the adjustments to within the specifications listed in the service manual, and your deck will perform as if it were new, fresh from the factory. In that condition, the NAD 6300 is famous for being able to make some of the finest recordings possible. If you are servicing someone else's deck, that's where you stop. It's performing to spec. #
- But for your personal deck, you can be extremely patient. You can get all those 0.5 dB differences down to 0.05 dB, or even less, and your recordings will be even better. (And if you're just learning, as I have been, you will do the entire sequence multiple times, just to be sure you understand what you are doing, and to ensure that repeated measurements let you know for a fact that you got it as close as is physically possible, and that you didn't stop just because you got tired or bored.) #
- The reason there are so many adjustments to make is that, in addition to having do do everything twice, once for the left channel, and once for the right, you have to do everything three more times, because there are three main types of cassette tape, and multiple adjustments to make for each of those. #
- To ensure that the magnetic particles, embedded within the thin, stretchy plastic carrier tape, take the maximum signal, the recording circuitry will add a high-frequency component to the signal. This high-frequency energy, outside the range of human hearing, is bias, which I think of as a way of overexciting the particles so they settle down more easily into the pattern we want. It establishes a baseline of energy, atop which the musical fluctuations ride.#
- There are three main types of cassette tape. Type I is "normal", type II is "chrome" and type IV is "metal". (Type III exists, but is rare.) They differ mostly in the kinds of particles embedded on the tape, and each requires a different amount of bias, and therefore a separate set of adjustments to the cassette deck. There is not just one "type I" tape, of course, there are different brands, such as TDK and Maxell. Each manufacturer made several variants, aimed at specific levels of performance and price. So a TDK D is different from a TDK AD, and differs from a Maxell UR, or Maxell UD XL-I, even though they're all type I tapes. Even the same type, from the same brand, can vary depending on when it was manufactured.#
- But you have to align your deck to an actual, physical, cassette, so you have to select one brand, and one formulation from that brand. Your deck will be aligned perfectly to record on that kind of tape. But because you will want to record on other brands and formulations, the NAD 6300 has a fine bias adjust knob on the front. If you're recording on the tape you used to align the deck, you leave it alone. But if you're recording on some other type of tape, you carefully adjust it for accurate treble reproduction. #
- I have signal generators, distortion analyzers, and spectrum analyzers, so eventually I'll get around to doing it right. But for now I am doing this part by ear. The other, critical, adjustment you make by ear is setting the recording level. This can be done with lab equipment, but we don't listen to test signals. #
- Sources vary in loudness, musical dynamics, high-frequency energy and bass. Tapes vary in their ability to take the magnetic flux. Some tapes can be recorded hotter before saturation distortion becomes audible. You want to record the maximum possible signal the tape will take, because the tape itself has some noise, a hiss, you can hear all by itself. The higher the signal you can put onto the tape, the louder the quietest parts of the music, the less hiss you can hear. #
- In addition to fine-tuning the bias circuitry during align meant, and the front-panel fine bias adjust, the NAD 6300 has two more features designed to maximize recording volume: HX Pro, which was an improvement to a Dolby design made by Bang & Olufsen, and DynEQ, which came from Tandberg. There aren't many decks made with both, which is one reason the NAD 6300 is unique. The result is that you can record a hotter signal to the tape, without distortion, than you otherwise can.#
- Cassette decks generally feature noise reduction, usually Dolby B and Dolby C. This is a process that modifies the signal before it gets to the tape, and there's a complementary process during playback that undoes the changes made during recording. The result is that the hiss, a high-pitched noise inherent in the tape itself, is pushed out of audible range. #
- Dolby B recordings are more common (the deck in my car can only decode Dolby B), and due to how the process manipulates high frequencies, some people like to listen to a B recording with the decoding process disabled. It makes it sound brighter. Dolby C recordings feature better noise reduction, up to 20 dB instead of the 10 dB provided by Dolby B, but you do not want to listen to a Dolby C recording without the Dolby C mode enabled, nor do you want to play it in Dolby B mode.#
- When you make a tape, you are recording a specific musical performance, a particular reality, as measured and imprinted by a unique combination of tape medium, capabilities, adjustments, settings and tunings, each of which you select. It is an individual act, resulting from a series of judgments you have made. You decide what music to record, onto which tape, using which device, and apply your knowledge, hearing and expertise, to create a real, physical thing, which only exists because you made it. What will you want to listen to next, the next time you play this cassette? What will you put on side one, what goes on side two? If it doesn't fit, and it never does, which songs get included, and which skipped?#
- I've spent New Years making some cassette recordings. They are on TDK SA-90, which is not the type II tape which I used to align the cassette deck. So I've tuned the fine bias control. I also took some time to set the recording level. The NAD 6300 is a three-head deck, which means as the tape goes by, one head erases, one records, and one plays back. This, along with the input monitor switch, lets you hear both what you're recording, and the actual playback from the tape, as you're doing the recording. However, playback can be a different volume than the source, and louder things sound better, so you still have to adjust the playback volume when switching back and forth to hear the differences properly.#
- These recordings are being made without noise reduction, because I discovered I could hear the difference in the brushed snares of a symphony orchestra going full blast, which is simultaneously a very loud sound, and a very subtle one. The detail was lost using Dolby C. That source was a Super Audio CD of the RCA Living Stereo 1959 and 1961 recording of Arthur Fiedler's Boston Pops Orchestra performing George Gershwin's Rhapsody in Blue. My goal is to record this performance, best I can, as if I were there, and recording the very event so I can listen to it later, as if I were there, crystallizing this experience into a single, physical, thing: the cassette.#
- A cassette is more than just the tape, that thing you put into the deck, which is a precision-made shell that contains the actual plastic tape, several spinning hubs, a tiny spring-loaded pressure pad, and slip sheets to minimize friction. Cassette tapes also come with a plastic case, which holds both the cassette and the J card. The J card identifies the tape and describes its contents. #
- In prerecorded tapes, it's a designed object, created with attention to colors, proportions, and appearance, just like the music itself, but generally by a graphic designer, rather than the musician. It's another representation of what is on the tape, in a different medium, print rather than sound.#
- It should tell you what's on the tape, so you can tell it apart from the other tapes. It should also tell you the settings for the tape, whether you play it back with noise reduction, and what type of tape equalization to use.#
- The J card can also contain production notes about the recording, such as the level the tape was recorded at, and any adjustments made to the fine bias. These can be useful for making better recordings next time. #
- The J card should tell you what's important to know about the tape. And it should be beautiful, in its own way, like the music. Like all graphic design, it should be pleasing to look at, and convey specific information. For these New Years recordings I chose to use photographs of the deck itself, in the act of recording, showing the positions of the knobs, printed on 4x6 glossy photographic paper, carefully trimmed and folded. I love the way these tapes sound, and I love the way they look. #
- In a very real sense, they literally are New Years Day, 2023. This is just like blogging, except when you're done, you've created a physical object, a cassette tape, a thing that exists, a captured musical event, a work of art.#
Monday January 2, 2023; 6:10 PM EST
- (11 min read)#
- #
- A cassette recording is not a copy. You can make an exact copy of a digital file, and each time you load that file you will get the exact same series of bytes. A cassette recording is literally a recording of a specific event. It is a record of reality, as it exists at that moment. It's the intersection of the audio signal, measured by a specific source device such as a Super Audio CD player, and captured by imposing magnetic flux onto a particular tape by a particular cassette deck. The recording is a captured performance of specific set of conditions, each of which contributes to the final sound. #
- Every cassette recording is literally unique in the universe. The cassette deck is a physical device, and mechanical devices are not perfect. Tape heads, capstans and pinch rollers get dirty. The motors spin as consistently as possible, but there is always wow and flutter. As a painter may work on a stretched canvas, or paper, or cardboard, the tape itself is also a physical medium. Each has its own characteristics, such as how much signal it can take, how much noise the tape itself provides, how much bias it takes to properly orient the tiny magnetic particles.#
- The final sound, at playback, is another performance, created in real time by a physical device, a cassette deck which measures the magnetic flux on the tape. This signal is amplified, and used to drive a preamplifier, amplifier, and then speakers or headphones. Every time you listen to a cassette, it is a specific, particular, unique, individual experience. A performance, a rendition of a specific reality, created in real time. #
- This weekend I have been making recordings from my NAD 6300 Monitor Series Cassette Deck. I spent the past several weeks aligning this deck. Most of the adjustments you make are related to recording, and the pots and variable capacitors are extremely sensitive to the smallest movements. Sometimes you're just applying pressure, rather than turning. And once you've made that feather touch, you record a test signal for ten seconds, adjust the test signal to a higher frequency, record another ten seconds. Then you rewind the tape, and play it back. #
- Measurements are taken from test points at the input to the Dolby circuitry, at the minimum levels you can record. Input around 6 mV results in a measurement of around 40 mV. You watch values change on the multimeter, which you have set to maximum digits, and adjust the meter's rate so it gets a steady value on the first frequency, and set that as your zero dB reference. Then you watch for the change in voltage at the higher frequency. You want the difference to be as small as possible. To be in spec, it should be within 0.5 dB. If it is not, make the adjustment again, and redo the recording.#
- Each individual nudge-record-adjust-frequency-measure cycle takes a minute or so. There are more than two dozen variable resistors and tuning filters to be adjusted, and it can easily take a dozen or more attempts before you get one into spec. These are resonant circuits, which means they have a specific point at which they are in tune, and you can't just turn a pot until it reaches maximum. Maximum will be somewhere in between the extremes, and that point will shift as you tune the other parts of the circuit. Some of the steps affect adjustments made in previous steps, so you go back and fine-tune those, another half-dozen more adjustments to something you've already tuned.#
- If you are patient, you can get all the adjustments to within the specifications listed in the service manual, and your deck will perform as if it were new, fresh from the factory. In that condition, the NAD 6300 is famous for being able to make some of the finest recordings possible. If you are servicing someone else's deck, that's where you stop. It's performing to spec. #
- But for your personal deck, you can be extremely patient. You can get all those 0.5 dB differences down to 0.05 dB, or even less, and your recordings will be even better. (And if you're just learning, as I have been, you will do the entire sequence multiple times, just to be sure you understand what you are doing, and to ensure that repeated measurements let you know for a fact that you got it as close as is physically possible, and that you didn't stop just because you got tired or bored.) #
- The reason there are so many adjustments to make is that, in addition to having do do everything twice, once for the left channel, and once for the right, you have to do everything three more times, because there are three main types of cassette tape, and multiple adjustments to make for each of those. #
- To ensure that the magnetic particles, embedded within the thin, stretchy plastic carrier tape, take the maximum signal, the recording circuitry will add a high-frequency component to the signal. This high-frequency energy, outside the range of human hearing, is bias, which I think of as a way of overexciting the particles so they settle down more easily into the pattern we want. It establishes a baseline of energy, atop which the musical fluctuations ride.#
- There are three main types of cassette tape. Type I is "normal", type II is "chrome" and type IV is "metal". (Type III exists, but is rare.) They differ mostly in the kinds of particles embedded on the tape, and each requires a different amount of bias, and therefore a separate set of adjustments to the cassette deck. There is not just one "type I" tape, of course, there are different brands, such as TDK and Maxell. Each manufacturer made several variants, aimed at specific levels of performance and price. So a TDK D is different from a TDK AD, and differs from a Maxell UR, or Maxell UD XL-I, even though they're all type I tapes. Even the same type, from the same brand, can vary depending on when it was manufactured.#
- But you have to align your deck to an actual, physical, cassette, so you have to select one brand, and one formulation from that brand. Your deck will be aligned perfectly to record on that kind of tape. But because you will want to record on other brands and formulations, the NAD 6300 has a fine bias adjust knob on the front. If you're recording on the tape you used to align the deck, you leave it alone. But if you're recording on some other type of tape, you carefully adjust it for accurate treble reproduction. #
- I have signal generators, distortion analyzers, and spectrum analyzers, so eventually I'll get around to doing it right. But for now I am doing this part by ear. The other, critical, adjustment you make by ear is setting the recording level. This can be done with lab equipment, but we don't listen to test signals. #
- Sources vary in loudness, musical dynamics, high-frequency energy and bass. Tapes vary in their ability to take the magnetic flux. Some tapes can be recorded hotter before saturation distortion becomes audible. You want to record the maximum possible signal the tape will take, because the tape itself has some noise, a hiss, you can hear all by itself. The higher the signal you can put onto the tape, the louder the quietest parts of the music, the less hiss you can hear. #
- In addition to fine-tuning the bias circuitry during align meant, and the front-panel fine bias adjust, the NAD 6300 has two more features designed to maximize recording volume: HX Pro, which was an improvement to a Dolby design made by Bang & Olufsen, and DynEQ, which came from Tandberg. There aren't many decks made with both, which is one reason the NAD 6300 is unique. The result is that you can record a hotter signal to the tape, without distortion, than you otherwise can.#
- Cassette decks generally feature noise reduction, usually Dolby B and Dolby C. This is a process that modifies the signal before it gets to the tape, and there's a complementary process during playback that undoes the changes made during recording. The result is that the hiss, a high-pitched noise inherent in the tape itself, is pushed out of audible range. #
- Dolby B recordings are more common (the deck in my car can only decode Dolby B), and due to how the process manipulates high frequencies, some people like to listen to a B recording with the decoding process disabled. It makes it sound brighter. Dolby C recordings feature better noise reduction, up to 20 dB instead of the 10 dB provided by Dolby B, but you do not want to listen to a Dolby C recording without the Dolby C mode enabled, nor do you want to play it in Dolby B mode.#
- When you make a tape, you are recording a specific musical performance, a particular reality, as measured and imprinted by a unique combination of tape medium, capabilities, adjustments, settings and tunings, each of which you select. It is an individual act, resulting from a series of judgments you have made. You decide what music to record, onto which tape, using which device, and apply your knowledge, hearing and expertise, to create a real, physical thing, which only exists because you made it. What will you want to listen to next, the next time you play this cassette? What will you put on side one, what goes on side two? If it doesn't fit, and it never does, which songs get included, and which skipped?#
- I've spent New Years making some cassette recordings. They are on TDK SA-90, which is not the type II tape which I used to align the cassette deck. So I've tuned the fine bias control. I also took some time to set the recording level. The NAD 6300 is a three-head deck, which means as the tape goes by, one head erases, one records, and one plays back. This, along with the input monitor switch, lets you hear both what you're recording, and the actual playback from the tape, as you're doing the recording. However, playback can be a different volume than the source, and louder things sound better, so you still have to adjust the playback volume when switching back and forth to hear the differences properly.#
- These recordings are being made without noise reduction, because I discovered I could hear the difference in the brushed snares of a symphony orchestra going full blast, which is simultaneously a very loud sound, and a very subtle one. The detail was lost using Dolby C. That source was a Super Audio CD of the RCA Living Stereo 1959 and 1961 recording of Arthur Fiedler's Boston Pops Orchestra performing George Gershwin's Rhapsody in Blue. My goal is to record this performance, best I can, as if I were there, and recording the very event so I can listen to it later, as if I were there, crystallizing this experience into a single, physical, thing: the cassette.#
- A cassette is more than just the tape, that thing you put into the deck, which is a precision-made shell that contains the actual plastic tape, several spinning hubs, a tiny spring-loaded pressure pad, and slip sheets to minimize friction. Cassette tapes also come with a plastic case, which holds both the cassette and the J card. The J card identifies the tape and describes its contents. #
- In prerecorded tapes, it's a designed object, created with attention to colors, proportions, and appearance, just like the music itself, but generally by a graphic designer, rather than the musician. It's another representation of what is on the tape, in a different medium, print rather than sound.#
- It should tell you what's on the tape, so you can tell it apart from the other tapes. It should also tell you the settings for the tape, whether you play it back with noise reduction, and what type of tape equalization to use.#
- The J card can also contain production notes about the recording, such as the level the tape was recorded at, and any adjustments made to the fine bias. These can be useful for making better recordings next time. #
- The J card should tell you what's important to know about the tape. And it should be beautiful, in its own way, like the music. Like all graphic design, it should be pleasing to look at, and convey specific information. For these New Years recordings I chose to use photographs of the deck itself, in the act of recording, showing the positions of the knobs, printed on 4x6 glossy photographic paper, carefully trimmed and folded. I love the way these tapes sound, and I love the way they look. #
- In a very real sense, they literally are New Years Day, 2023. This is just like blogging, except when you're done, you've created a physical object, a cassette tape, a thing that exists, a captured musical event, a work of art.#