What factors besides the EQ curve affect the sound of a record — an overview of the signal chain from recording to cutting

What factors besides the EQ curve affect the sound of a record?

Question answered on this page: What elements make up the signal chain from recording to cutting, beyond the EQ curve, and how does each one affect the sound?

The signal chain passes through a great many stages

The sound carved into a record's groove is the result of live sound in the studio passing through a long signal chain. Pt.24 examines the elements of this signal chain in detail.

Here, the major stages that affect the frequency response of the sound are organized into seven categories.

1. Microphone characteristics

Frequency response varies significantly from one microphone model to another.

For example, the Western Electric 394 condenser microphone, widely used in the 1930s and 1940s, had a peak of approximately +10 dB around 3.5 kHz. By contrast, the RCA 44-BX ribbon microphone had a relatively flat response.

Even recording the same piece in the same studio, a different microphone will change the frequency balance. This single stage alone can produce tonal differences comparable to — or even greater than — the difference between EQ curves.

2. Studio acoustics and microphone placement

The reverb characteristics of the studio, the distance and angle between microphones and instruments, and the acoustics of the recording venue itself all affect the captured sound.

In classical music recording in particular, the choice of hall and microphone placement can have a decisive influence on the final sound.

3. Program EQ, compressors, and limiters

At each stage of recording, mixing, and mastering, engineers intentionally shape the sound.

• Program equalizer — a variable equalizer, typified by the Pultec EQP-1A, used to boost or cut specific frequency bands
• Compressor / limiter — controls dynamic range
• De-esser — reduces sibilance
• Echo chamber / reverb — adds reverberation. Widely used in popular music recording from the 1940s onward, including physical reverb rooms (echo chambers) built into studios, as well as devices such as plate reverbs (EMT 140), spring echoes, and tape echoes. Although not primarily intended to alter frequency response, these significantly affect the overall impression of the sound

In popular music and jazz, the use of these devices for tonal shaping was common practice. Classical music recording is generally considered to involve less processing, though microphone preamp EQ and compressors were still used on occasion.

4. Tape recording EQ

From the 1950s onward, as master tape recording became standard, the recording and playback characteristics of the tape recorder itself (tape EQ standards such as CCIR and NAB) became part of the signal chain.

The type of tape, recording speed, and bias settings all affect the high-frequency response and noise floor.

5. Disc recording EQ (phono EQ curve)

This is the stage at the center of the EQ curve debate. The three parameters — turnover frequency, high-frequency pre-emphasis, and bass shelf — determine the frequency response applied during cutting.

However, as we have seen, this stage is just one part of the overall signal chain.

6. Cutter head characteristics and diameter EQ

Each cutter head model has its own inherent frequency response. Additionally, before hot stylus technology became common — particularly in the era of broadcast transcription discs and acetate discs — the decreasing linear velocity toward the inner grooves caused high-frequency degradation, so "diameter EQ" (inner-groove compensation) was sometimes applied to correct for this.

Furthermore, when cutting stereo LPs, a process known as LFX (Low Frequency Crossover) or EE (Elliptical Equalizer) is sometimes applied. Instead of using a high-pass filter to cut the very low frequencies, LFX blends the low-frequency stereo signal into mono, preventing groove lifting and other cutting errors.

7. Pressing and playback environment

The process of creating a stamper from the cut lacquer disc and pressing it onto vinyl can introduce subtle changes in characteristics. Furthermore, on the playback side, the cartridge, amplifier, speakers, and room acoustics all determine the sound that ultimately reaches the listener's ears. It is also known that the phono equalizers built into amplifiers varied more than one might expect from manufacturer to manufacturer and model to model (→ Pt.23).

Concrete examples: how different engineers shaped the signal chain

The influence of program EQ: Contemporary Records — Steve Hoffman, drawing on his experience remastering approximately 40 Contemporary jazz titles, has stated that "most could be cut directly from the master tapes without any issues." However, for certain recordings (those from around 1957 engineered by Howard Holzer), he found an unnatural boost in the upper midrange that required a correction of 1–3 dB from around 6 kHz. This correction was not due to a difference in EQ curves, but to tonal shaping through program EQ (category 3).

Creative use of tape EQ: Roy DuNann — Contemporary Records engineer Roy DuNann is said to have recorded at a tape speed of 15 ips but intentionally used the recording curve for 7.5 ips (which applies stronger high-frequency pre-emphasis), then de-emphasized it during cutting — effectively practicing his own form of noise reduction. This was a creative application of tape EQ (category 4) in the era before Dolby.

The entire signal chain shaping the sound: Rudy Van Gelder — Mastering engineer Steve Hoffman has analyzed Van Gelder's recordings as follows: "Take three or four expensive German mics with a blistering top-end boost, put them real close to the instruments, add some extra distortion from a cheap overloading mic preamp, put some crappy plate reverb on it, and record. Then, immediately redub the master onto a tape deck at +6 dB, compress the crap out of it while adding 5 dB at 5000 cycles to everything."

(Hoffman's comment is aggressive in tone, but the point of interest here is solely how the signal chain shaped the sound.)

What this description illustrates is that multiple stages of the signal chain — microphone characteristics (category 1), program EQ, compression, and reverb (category 3), and tape dubbing (category 4) — combined to create a single distinctive "sound." This is precisely the kind of sonic difference that cannot be explained by the EQ curve alone.

Differences by genre

How much each stage of the signal chain affects the sound varies by genre.

• Classical music — program EQ and compressor use is relatively restrained. Differences in EQ curves may be comparatively easier to hear
• Jazz / popular music — diverse tonal shaping is applied, varying by studio and by engineer. It is difficult to reduce the discussion to EQ curves alone

Summary: the EQ curve is one part of the whole

The EQ curve is an important stage in the signal chain from recording to cutting, but it is not the only one.

Attempting to arrive at the "correct sound" by changing only the playback EQ curve has inherent limitations. This does not diminish the value of studying the history of EQ curves — rather, it provides the necessary context for understanding the history of recorded sound in a broader perspective.

→ EQ curve vs. mastering — which determines the sound? — for a conceptual overview

→ Can you hear a difference when you change the EQ curve?

For details → Pt.24

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