Bright to Muddy - Why and how do I correct it?

[James]

Some of my postwar 78's start out at a certain level of "brightness" and then slowly get more and more "muddy" in their sound. My tracking and such is fine. What causes this and how is it corrected?

[Rick]

Re: Bright to Muddy - Why and how do I correct it?

James
Not sure exactly. I do know that the tangential velocity of the needle is greater at the start of a recording than at the end, so there is change in high frequency response that will naturally occur. It will be best at the start of the recording and get worse twards the end. This is often noticable in the character of the noise from start to finish.
You could do selective processing to add more high end boost (or less cut) towards the end of the record.


Rick Carlson

[quartet87]

Re: Bright to Muddy - Why and how do I correct it?

I understand that as far as lp's go, the basic mastering m.o. was to slowly increase the high end of inner tracks to compensate for the natural high end degration as the stylus tracked toward the center. I'm wondering if these 78's were mastered without any compensation.

-Danny Gilbert

[Dan McDonald]

Re: Bright to Muddy - Why and how do I correct it?

Just goes to show that Edison was right in holding on to cylinders for so long.. I assume they don't have the problem, since they stay at a constant rate of travel.

Dan

[greg_m]

Re: Bright to Muddy - Why and how do I correct it?

Most 78's were probably mastered with no compensation (Certainly the acoustic 78's had no compensation!). If you look up EQ curves they usually relate to various brands and/or dates of LPs.

Indeed, a variable "diameter equalizer" was used when cutting 33rpm phonograph records (at least at some point in time). It used a special rotary attenuator; in place of a manually operated knob there was a small "pulley"; a cord wrapped around the pulley "is attached to the cutting-head carriage." The HF boost was quite pronounced: with a groove diameter of 4", the boost at 10 kHz was about +8.5 dB! (Of course this is for a 33rpm microgroove disc.) [Audio Cyclopedia, Howard M. Tremaine, Howard W. Sams & Co., Second Edition, 1974, pp. 668-670.]

One school of thought was that the spiral should start at the center, and spiral toward the outside; most symphonic material (for example) starts rather low in level with perhaps less HF information (bow/blow more gently and produce less harmonic content); then becomes progressively louder/brighter; thus it would be more appropriate to record the louder/brighter content in the best part of the disc, the largest diameter.

In fact, some old broadcast transcriptions were cut this way.

One good argument for cutting outside in is that if you're cutting something short, you can use the best part of the disc; if you're cutting something short (or of somewhat unknown length), and start at the inside, you'll use the worst part of the disc.

At any rate, the industry eventually standardized on discs that are cut from the outside inward.

(BTW, CD's are grooved inside outward, but since they are CLV, rather than CAV, it doesn't matter.)